To both of you, this is a VERY, VERY common occurrence for either a brand new baby who has only been home for a few days (can suffer from relocation stress for up to 2 weeks) and for a baby who seemed to be doing well for weeks after the relocation stress period passed, but then started to act very lethargic and stopped eating.
So to the second poster who has only had their baby dragon for a couple of day, yes it may very well still be relocation stress, as I said this can last up to 2 weeks. HOWEVER, that being said, you may then end up just like the Original Poster, who's Dragon got through the relocation stress period, ate well and was very active and was acting normal for weeks, and then suddenly they became very lethargic and stopped eating. So please do make your own post in the ER and post photos of your baby as well as her entire enclosure and setup, including the lights, and please list exactly what
UVB light and what Basking light you are using, list the Basking Spot Surface Temperature, the Hot Side Ambient (air) Temperature, and the Cool Side Ambient (air) Temperature, and what type of thermometer you are using to measure the temperatures with (stick-on, Digital with a Probe, or a Temperature Gun).
To the OP, it's very likely that your baby has stopped eating and become very lethargic because #1.) The
UVB light that you are using is either inadequate, is being obstructed by a mesh lid on the enclosure or a clear plastic cover on the fixture that is covering the UVB tube, or both, your
UVB light is mounted too far away from her main Basking Spot/Platform, or your
UVB light is older than 6 months old, OR A COMBINATION OF ALL OF THESE (usually is a combination of all of these), OR #2.) The 3 Temperature Zones within your enclosure/tank are not within the correct ranges (Basking Spot Surface Temp between 105-110, Hot Side Ambient (air) Temp between 88-93, and Cool Side Ambient (air) Temp between 75-80), or you're using only stick-on thermometers which are very inaccurate, usually off by between 10-20 degrees, and which you cannot measure her Basking Spot Surface Temperature at all with, only Ambient (air) temperatures with......
There are several other little things that can cause issues, such as using a loose substrate in the bottom of a baby or juvenile's enclosure/tank, like ANY type of sand (playsand/regular sand or any type of "Calcium Sand" like Calcisand, Reptisand, Bearded Dragon Sand, etc., all are the same thing), Crushed Walnut Shells (the absolute worst substrate for any reptile), gravel/aquarium gravel, rocks, any type of seed like millet seeds, pellets, wood chips, bark, ReptiBark, rodent bedding, or any other Loose Substrate which can and will very easily cause a little baby or juvenile to become severely impacted or even cause an actual Bowel Obstruction in the case of any type of Calcium Sand, Crushed Walnut Shells, or gravel/rocks...
Another issue is feeding them mealworms, baby and juvenile dragons should NEVER be fed any mealworms for the same reasons they shouldn't have loose substrates. Mealworms are mostly made up of a very hard, Chitlin shell that might as well be made of rocks, because they cannot digest them fully, and in small babies and juveniles they very often cause severe impactions or Bowel Obstruction. In addition, even though large, adult Dragons can digest mealworm shells a bit better than babies and juveniles, mealworms should never be fed as a "Staple" live insect, as there is absolutely no nutritional benefit to doing so. What little part of a mealworm isn't the hard, Chitlin shell is mostly fat, they contain very little protein and even fewer essential vitamins or minerals. Their Calcium content is negligible and so is their Vitamin B1 (Thiamine) content, as opposed to the multiple healthy "Staple" live feeder insects that you should be feeding your dragons, which include Crickets, Dubias and other species of Roaches,PhoenixWorms/BSFL/Reptiworms/CalciWorms/NutriGrubs (all exactly the same thing, just different brand names), and Silkworms, which can now be purchased in Bulk quantities online from Amazon.com (Most online companies that sell live feeder insects in bulk quantities inexpensively that most of us order from are always "Out of Stock" of live Silkworms and only have bulk Silkworm eggs in stock if you want to raise/breed them yourself, which is very inexpensive to do, but it takes a long time to get them up to feeding size). I was very pleased to find out that there are ample quantities of live Silkworms in multiple sizes on Amazon.com.
So if you could please post some photos of your baby, her entire enclosure/tank and her lighting, and then list what
UVB light and what Basking light you have in detail, and then answer the questions above, such as whether or not the
UVB light is being obstructed by a mesh lid and how far away in inches it is from her Basking Spot/Platform, etc. then we can try to pinpoint the issue for you. I'm glad you came here for help, as this is really a serious issue for people buying Bearded Dragon babies who are new owners. Unfortunately it seems as though pet shop employees have not a clue what they're talking about as far as Bearded Dragon lighting, temps, and general husbandry and diet goes (and I'm not just talking about Petco and PetSmart, we've had MANY people who bought their dragons from "Reptile Specialty Pet Shops" who have gotten horrible advice and who were sold the wrong equipment or just a bunch of totally unnecessary equipment).