Is my beardie too small?

I got my bearded dragon at the beginning of August last year when he was 2 months old. That means that he is 12 months old. He hasn't gained much weight in the last 4 or 5 months and it kind of worries me. I know his weight gain should slow down around this time, but every other adult dragon I see is about twice his size. He's currently about 15 1/2 inches, which I think is about right, but his body is smaller than all the ones I see in the store. I don't have a scale small enough to weigh him. His head is considerably smaller than the ones on the adults in the stores I go to, and he isn't as gurthy either.
I do let him run around my office while I'm working, and I'm pretty sure his chest is a little buffer than the ones in the store, could the exercise cause him to be skinnier?
I have a strip light for UVB that the owner of the reptile store in my area recommended. I also have another light that is a UV light. I have a red heat light that stays on all day and all night too, so I think he's getting the proper light and heat that he needs. He can get right under the heat and all the way out of it. During the day, the warmest area is about 100 degrees and the coolest is about 70 degrees. At night, the warmest is about 80 degrees, and the coolest is about 70.
I have crickets delivered to my apartment by the thousands, and I feed him about 30 or so a day. He usually doesn't eat them all, so I'm pretty sure he's eating enough. I shake the crickets in a bag with calcum power every day. I skip the calcium once every couple weeks or so. Right now I'm giving him collard greens every day as well. He used to eat mostly carrots, and he gets zuccini every now and then. I don't dust with a vitamin powder though. Could that be a problem? I feed him in the late morning.
His poop is not a solid either. It's pretty diarreah-like. I took him to the vet in mid March to see if he had some sort of parasite, and the made him poop, and said they were worried that he might have pin worms, but when they checked the poop they said that he was fine, and that he just had a lot of flagellates in his poop. (I'm pretty sure she said flagellates) Anyway, she perscribed Metronidazole for 10 days, which made his poop more solid, but now it's back to runny. It's been runny most of his life, and I don't think it's normal, but other than that and his weight, he seems fine. He used to poop a lot for his size, kind of like the food was going right through him. Do you think that's a sign of a problem?
When I first got him I had him in a 10 gal tank with a felt type bottom for a couple months, then I bought a 125 gal tank and now I use calcium sand. He doesn't get to use the whole tank yet because I give him more and more room as he grows and I think he needs to grow more.
I don't bathe him, but I did put him in a large tupperware thing with warm water in it once when he was on medication for his poop. It wasn't too deep of water, and he didn't really like it. I used to mist him with a water bottle all the time when he was a baby, but as he grew up, I didn't mist him as much.
He's my first reptile, so all the lights, and food supplements, and live food are all new to me, I'm getting better at it, but I still think something is wrong... it just doesn't seem right and I can't figure out what it is. Does he seem like he's growing normally, and healthy?

Ok so there are alot of things that could be wrong, so ill start from the beginning.

Firstly the lighting. You said you have a UVB strip and another UV bulb?? The brands of the UVB are extremely important, as there are many 'recommended' by pet shop/breeders not because they are good but the profit margins are better! many can actually cause alot of damage! How old is the bulb? they need to be changed every 6 months as although they turn on the amount of UVB produced whittles down to nearly nothing after 6 months. Desert lizards such as beardies need ALOT of UVB. That being said there is a thing as too much, so one bulb only! The only brands i would recommend are the reptiSUN 10 (not reptiGLO), and if in the UK Arcadia 12%

They will also need a bright white UVB bulb for basking, the red bulb will not protect his eyes from the strong UVB bulb. This needs to be placed alongside the UVB bulb (which runs the length of the tank) and should be turned on at the same time as the UVB bulb (so depending on the season around 12 hours). All lights should be turned off at night. Beardies need dark to sleep, and they need to cool off during the night. the red light will not only be keeping him too warm, but he wont be getting a proper sleep. If the temp drops below 65f at night you can get a ceramic heat emitter which dosnt produce light. If it stays above 65f you dont need anything at all.

The basking temp is a little low, you need 100-105f but it all depends how you are measuring them with, the round dial type one can be up to 20f off so its important that you either have a digital one with a long probe, or a temperature gun.

Also the calcium sand i would remove. again pet shops recommend it, even though it says how harmful it is on the package! Beardies like to lick and when they ingest sands, esp calicsand it solidifies and blocks up the inside. He is still pooping which is good, but sand is like a litter box, so ill bet he has parasites again. Slate tiles or reptile carpet are much better for them and much easier for you to clean. If you adamant you want sand, only use washed kids playsand (for sand pits) and you need to spot clean it daily and completely change it weekly to avoid parasite problems.

Baths take some getting used to but its important to keep them hydrated, so once or twice a week just pop him in water (up to the arm pits and luke warm) for 20 min. He will get used to it, even love it!

i think thats it, so i would change the lighting around, you can also let him have the whole tank, im sure he would like the space! and get another fecal test done. Its a good idea next time once they've gone through treatment, to get a second test done to make sure its all worked

B

So the strip light is ReptiSUN 10 and the other light is a 75w "Basking Spot Lamp" made by ZOO MED. I was using the red light because when I checked the temperature on his basking spot during the day, it wasn't warm enough, and our apartment gets super cold at night... probably around the 60-65 area, and I've read in bearded dragon books that it should not get colder than 75 degrees in there. I also heard that lizzards can't see red, so the light doesn't bother them... was I wrong? The red heat one is 100w "Heat Glow" by EXO TERRA. I figured that the brand didn't matter because heat was heat and he couldn't see it. All these lights really confuse me.

I'm going to be moving soon (like within a week or so) so I was planning on giving him the rest of his tank then. I just bought 80 more pounds of calcium sand a couple weeks ago for when we move, so after that, I'll start using something else. How do you feel about the ZOO MED "Eco Carpet" that's what was recommended by the pet store I bought him from to use for the first year, but then I found a reptile store (he sold me the ReptiSUN 10) and that guy said that It was fine to use sand, but that I wanted calcium sand. He's a small store owner, and is very knowledgable about his stuff, and every now and then I'll look at something in his store and he'll tell me not to buy it... (but that could be his plan to make me trust him...hemm... I havn't been able to go back to the place that I bought him from for advice because their reptile room caught on fire, and they havn't been in business for about 6 months now, they're coming back though...

Anyway, please let me know and I'll take a stool sample to the vet. He's very moody about how and where he poops. I let him run around my office (he has a basking lamp hanging from under my desk with a rock underneath to sit on. The rock retains heat pretty well) and he runs and runs, and when he gets cold, he runs back to his light to warm up. Anyway, he likes to poop on my office floor, and doesn't like to poop in his tank. I try to take him out for a hour of two every day if i can, but he's held it for about 4 or 5 days once, waiting for me to take him out. Now he'll only wait a few days (depends on how full his belly is) before he'll poop in his tank. Does that seem odd?

No not really, mine will only poop in the bath! hwy dont you do a little experiment, drop a small bit of water on the sand. Calcium sand cloggs up alot more than normal sand, cement like. Just search the forums here and you will find many people who have had beardies die due to the sand. I would try and get a refund asap if youve already bought a big one.

They can see red lights, and blue, and black, so anything will disturb them at night.

When he poops just pop it in a bag or small box and take it into the vet. what were you measuring the temps with??

I don't really know what to call it, but it's round and I just set it where I want it to read the temperature, and leave it there a little bit, and it tells me. There's a dial that moves to the right number, it's not digital. They're all over, I can't believe I can't think of what their called...

yes i thought so, those dial type ones can be up to 20f off, so you may be either too hot, or too cold. They need exact temps in order to digest peoperly. Walmart sells a very good one in the outdoor therm section for $12, or you get get one online. You put the long probe directly on the basking spot and leave ot for 45 min to get a acurite reading!