Welcome to the forum, and I'm sorry Keith isn't doing very well, but we can definitely help you out. I've got to start out telling you that if you've had Keith for 5 months, and you bought him at a pet shop (who usually sell small babies that are around a month old) and he was older than a new month-old baby like they usually sell, then he's got to be at the very least 6 months, probably 7-8 months. And at 9 inches long and at the very least 6 months old, most likely older, he's very stunted in size. I agree with Tracie that he isn't digesting his food well, and his diet is not appropriate for him in the first place (superworms are not an adequate daily "staple" live insect for beardies, they are loaded with fat and little protein)...so you've got some serious husbandry issues going on related to #1) Improper temperature zones inside his tank, and #2) Inadequate UVB lighting, and then #3) Improper diet.
First of all, it's nearly impossible to establish a proper Bearded Dragon Temperature gradient inside a 10 gallon tank, it's just not large enough. Are you using only a stick-on thermometer? The reason I ask is that you only listed 2 temperature zones, both "Ambient", or air temperatures, and not a Basking Spot/Platform Temperature, which is a "Surface" temperature that you cannot measure with any type of stick-on thermometer. You either need a $10 Digital Probe Thermometer with a Probe you can sit right on his Basking Spot/Platform, or an infrared Temp Gun that you can aim right at the Basking Spot. For a Bearded Dragon, being a Desert Reptile that has very strict and specific temperature and lighting needs in order to digest their food, absorb the nutrition from the food, and then be able to process/use the nutrition in their bodies, you must have pretty exact temperature zones within their tanks, and a 10 gallon tank doesn't allow for that at all. So if you have a larger tank for him already then you need to get him in it and get it set up properly ASAP.
So the main factor that effects a Bearded Dragon "Digesting" their food properly is them having 3 temperature zones set up inside their tanks that are within the appropriate ranges, specifically the Basking Spot Surface Temp is the one that determines whether or not they can properly digest anything that they eat. You also have to make sure that they are not only within proper temperature zones, but that they are getting adequate UVB/UVA light, and that their daily photoperiod is at least 13-14 hours every single day under both a long, strong, adequate UVB tube that is at least a 10% UVB tube that is at least 18" long, and his bright-white colored Basking Bulb (you cannot use any colored bulbs at all for a Bearded Dragon, such as red, blue, green, purple, black, etc., only a bright white Basking Bulb is appropriate, as it replicates natural sunlight when combined with an adequate UVb tube), which is the adequate wattage to keep the temperature zones (at least the 2 within the Hot Side of the tank) within the correct temperature ranges. If they are too low they cannot digest their food properly, if they are too high it will not only dehydrate them, but it can be fatal over time.
BASKING SPOT SURFACE TEMPERATURE (within the Hot Side of the tank, positioned directly under BOTH the long UVB tube AND the bright-white colored Basking Bulb): Between 105-110 degrees F for a baby/juvenile under a year to a year and a half old; between 100-105 for an adult that is over a year or so old.
HOT SIDE AMBIENT (air) TEMPERATURE (The air temperature of the Hot Side of the tank which surrounds the basking spot/platform): Between 88-93 degrees F maximum.
COOL SIDE AMBIENT (air) TEMPERATURE (The air temperature of the Cool Side of the tank, opposite the Hot Side of the tank): Between 75-80 degrees F maximum; must be at 80 degrees maximum, as he must always have an area to go to that is considerably cooler than the Hot Side Ambient temperature.
*******So the thing that is a red-flag right away to me is that you listed the "Hot Side of the tank" as being around 100 degrees F. If you are only using a stick-on thermometer then this is actually the Hot Side Ambient Temperature, which should be a maximum of 93 degrees F. So if this is the case, then this typically means that his Basking Spot Surface Temperature is much hotter than the Hot Side Ambient Temperature around it, most likely well over 110 degrees, which should be the hottest temperature anywhere in the tank. So he could be extremely dehydrated or simply avoiding his basking spot because it's too hot, and this could be why he's not digesting his food correctly.
However, if you do have a Digital Probe Thermometer or an Infrared Temperature Gun, and the "100 degrees F" you listed for the Hot Side of the tank is actually the Basking Spot Surface Temperature, then it's too low, and this is why he's not properly digesting his food.
So that's the first problem, and honestly the only way to resolve this problem is to put him in a larger tank ASAP, one that is able to establish a proper Bearded Dragon Temperature Gradient with 3 distinct Temperature Zones inside it for him. A 20-Gallon LONG tank is the bare minimum size it seems to take in order to be able to establish a proper temperature gradient for a Bearded Dragon, and have the gradient stay pretty steady. However, in reality the minimum tank size for a 6 month old juvenile Beardie and older is a 40-Gallon BREEDER tank (not a 40-Gallon aquarium, but it must be a "Breeder Tank", as Bearded Dragons aren't really climbing reptiles, not to the extent that others are, and you need a tank/enclosure that is longer and wider than it is tall; it can be extremely difficult to get adequate UVB and UVA light to a bearded dragon in a tank that is tall, so this is why you have to use a 40-gallon BREEDER tank). Dragons complete around 85-90% of their total growth and development during their first year of life, and the rest during their second year of life, so they are "officially" considered to be adults at 2 years of age. Most experienced owners and breeders will agree that a Bearded Dragon who is between 1 and a half to 2 years old requires a larger enclosure with a minimum size of 4'x2'x2' as their permanent home. Either way, you absolutely must get him into a much larger tank than what he's in, it's effecting his health in a negative way which is severely stunting his growth...
For example, I have a male dragon right now that I got when he was 4 weeks old (I was helping the people who rescued 3 clutches of eggs out by taking him younger than they wanted to sell him, but they had taken in about 70 fertile eggs in out of the goodness of their heart). he's now a little over 7 months old, so either the same age as your dragon, or maybe even a bit younger than your dragon. He is now over 16" in length and last month at a visit with my CRV he weighed 382 grams. I also have a female dragon who I bought at my local Petco when she was a month-old baby who was around 5" or so long (so only 4" or so shorter than your dragon is now), and she's now about a year and 3 weeks old, and she's 21" long and weighs around 520 grams. Now I put both of them, as well as the male dragon I had prior to both of them (he died at just shy of 13 years old and I got him when he was a 2 month old baby) in either a very large, glass Exo Terra tank (a little larger than a 40-gallon Breeder tank is) or in a custom wooden enclosure that was either 4'x2'x2' or 4'x3'x2'. There shouldn't be any problem at all with keeping a very small baby dragon in a large tank, some people for whatever reason think that a large tank will be "too stressful" for a month old baby, but they don't ever consider that wild baby dragons in the Australian Desert are hatched and live on their own from day one in a vast, open Desert! So as long as you ensure that they have adequate UVB/UVA lighting and proper temperature zones, they'll be fine. That's key.
****The second issue I think you are having is most likely inadequate UVB lighting, either due to using a totally inadequate
UVB light in the first place, or due to having your UVB tube set up improperly. You said that you have a Reptisun 10.0
UVB light, but which one? Is it either the compact or coil version (regular lightbulb shape/size that fits into a regular lightbulb socket)? If so, then it's totally inadequate for a Bearded Dragon or any other Desert Reptile, and this is a very common mistake that new owners of Dragons make. They read "Reptisun 10.0" is a good
UVB light for a Bearded Dragon, so they go out and buy the compact/coil version and put it in either a Deep-Dome lamp or a Clamp-Lamp that is on top of the mesh lid to the tank. So if this is the case then your dragon has basically gotten no UVB or UVA light at all since you put him under that light.
The Reptisun 10.0 compact/coil
UVB bulb is only a 13 watt bulb, which is almost half of the wattage a Bearded Dragon needs to begin with. It's a great UVB/UVA bulb for a Tropical Reptile who doesn't need 13-14 hours of strong, intense, adequate percentage/wavelength of UVB and UVA light, but not even close to adequate for a Bearded Dragon. Then on top of the compact/coil version of that
UVB light being way too weak for a Dragon to begin with, most people put it in a light fixture and have it being obstructed by a mesh tank lid, which is going to block around 40% of the
UVB light emitted by the already far too weak
UVb bulb. Then on top of this (already the dragon is getting basically zero
UVB light at this point) they have this bulb further away from the basking spot/platform than is appropriate for that bulb, which honestly would have to be within 3-4" of the basking spot/platform and totally unobstructed by anything for it to get any appropriate UVB or UVA light to the dragon.
If the Reptisun 10.0
UVB light you have is a long, fluorescent tube that is inside a matching length fluorescent tube fixture, which it absolutely must be to be appropriate for a Bearded Dragon, then you must take note of what "Strength" of UVB tube it is. There are 2 basic strengths of UVB tubes, the much weaker and more commonly found in pet shops T8 strength, and the much stronger and really what a Dragon needs T5 strength. The most common Reptisun 10.0 UVB TUBE you will find in pet shops such as Petco or Petsmart is the 18" T8 UVb tube, which is a 15 watt UVB tube. While it's a pretty weak tube, it can still be made to be totally adequate for a Bearded Dragon, but the main mistake that people make when using the Reptisun 10.0 T8 UVB tube is that they set the tube fixture on top of the mesh lid to the tank, and in addition this usually makes the T8 UVB tube be further away from the basking spot/platform than is adequate for the T8 UVB tubes, which is 6" away from the basking spot/platform at a maximum. Either way, if you have a T8 strength UVb tube sitting on top of a mesh tank lid that is blocking around 40% of the
UVB light emitted by the tube, the T8 tubes are just not strong enough to have 40% of their
UVb light be blocked, and then still get adequate
UVB light to your dragon on the opposite side of the mesh, even if the basking spot/platform is within at least 6" of the tube on top of the mesh. As a result, we see dozens and dozens of dragons, usually between 6 months to a year old, who have started to exhibit signs of a Calcium deficiency and MBD, and they can't figure out why because they're using a Reptisun 10.0
UVB light, which is supposed to be great for dragons. Ultimately the problem is #1) They are using the compact/coil version that is totally inadequate, or #2) They are using the weaker T8 tube version and have it sitting on top of the mesh lid. Either way, the end result is always the same.
(Also, any and all T8 strength UVB tubes must be replaced once every 6 months at a maximum time period, as they have a very fast UVB decay rate, and at 6 months old they stop emitting any
UVB light and are only putting out regular "light").
If by chance you do have the Reptisun 10.0 T5HO UVB tube, then it is the tube you want, and it is strong enough to sit on top of the mesh lid as long as it is within at least 11" of the basking spot/platform and is not older than 12 months old. I doubt you have the T5HO version, only because you didn't state that, and usually people do.
Without any adequate
UVB light for 13-14 hours every single day, a Bearded Dragon's body cannot absorb any nutrition from their food or supplements that you give them, including any calcium. So they start to develop a severe calcium deficiency pretty quickly without adequate UVb and UVA light, which leads to a continuous weakening of their bone density, and starts the development of MBD. In addition, they aren't able to absorb much nutrition in general, and this is the #1 cause of stunted growth.
That's him beside a poo he had about a week ago (So you can see how big he is. I have no idea how old he is. The reptile store sold him as a juvenile and he's been with me about five months) 
The above poo close up
The very worrying poo he took this morning after a bath
He either stays under it or hides in his rock. 
