If you only just got him, he's likely still settling in.
BUT JUST IN CASE
Please give us a DETAILED and THOROUGH rundown of your feeding schedule and other husbandry aspects .
Might be a very easy fix .
Photos of the tank and showing substrate and lighting and of the beardie will help too. Use XIMG button to upload photos from your computer.
How heavy is he?
...... recommend weighing him regularly (weekly say)?
Can you give us a good rundown on the setup and schedules (light and feeding) :
TEMPERATURES ?
........daytime warm zone
........overnight
........basking spot
........ how are you measuring your temperatures ?
TOO COLD = SLEEPY DRAGON
UVA AND UVB ADEQUATE ?
........is the uv rated AT LEAST 10%UVB ?
........is it a COMPACT (curly globe & WATTAGE ?
or a T8 tube ?
or a T5 tube ?
or an MVB ?
........the brand (not all UVB compacts and tubes are created equal or as well , many shops sell their own brand (Zilla, All Living Things, Reptile-One, Nat Geo , Natural Selections (in green boxes) which are cheap Chinese clones made very cheaply using very poor quality quartz glass and cheap phosphors ==> very poor UV spectrum produced incl UVC band and bad parts of the UVB band)
........is it covered (in a domestic fluorescent light fitting )? == BAD
........is it sitting ontop a mesh top ? == BAD
........how far from basking spot ?
too far and the UVA and UVB WILL BE TOO DILUTE.
UVA FLUX TOO LOW where dragon is ==> a very lethargic dragon w/ a very poor apetite just in the short term ,
and neurological problems if this persists ,
not to mention MVB if UVB flux too low long enough with inadequate metabolisation of dietary calcium or inadequate intake out calcium
TANK
....... size (L x W x H) and construction , photos of the setup are often helpful .
SUBSTRATE ?
........is it sand ? == BAD AND IF CALCISAND this is EXTREMELY BAD/LETHAL when ingested.
........is it particulate ? == BAD
SHARING TANK ? == BAD
TOO SHORT A PHOTOPERIOD (lights are not kept on long enough each day , will make beardie think it is winter , recommend at least 14 HRS PER DAY)
FEEDING SCHEDULE (I recommend at least 2 hrs lights/heat on before first live feed and after last feed of the day)
....... when are you offering live feeder insects ? what are they ? how big are they ?
....... when are you offering greens and other veg ? what are you offering ?
What season is it (there where you live) ?
and
weather can have an impact on your beardie's behavior, so what had the weather been like in the problem period ?