I went through this with my girl when I first got her. I bought her from a Petco, and it turned out that she has adenovirus, which is an incurable virus that attacks the immune system and liver. She caught it from other infected beardies at the pet store or at the distribution center. It's actually VERY common among pet store dragons.
Now, I don't want to panic you with my story because it could be a number of things causing her lack of appetite. Can you give us a rundown of his tank setup? Please include the following:
1. Name and type of
UVB bulb (compacts are no good, so you will want a tube):
2. Type of basking bulb (should be a clear white incandescent bulb):
3. Substrate (tile is recommended, carpet is okay, but sand and any kind of loose substrate can cause impaction):
4. Feeders used and size (gutloaded crickets, roaches, silkworms, and BSFL are recommended, and they should be no bigger than the space between his eyes):
5. Nighttime temps (should be around 75. Do not use a nighttime bulb as it will bother him and distort his sleep cycle. a ceramic heat emitter is recommended if you need to increase the heat at night):
The basking temp range should be 105-115 for a juvenille. 98 is too cold. You also want to make sure you are alternating days with calcium + D3 and a multivitamin. I do 3 days of each per week and have one off-day. All of this is relevant to appetite. If any one of these is off, your little guy's metabolism may not function properly. I went from having a beardie who ate at MOST 10 small crickets a day to one who will eat 60+ large crickets a day. It all makes a difference! Also, I would suggest a well visit to a good reptile vet. Had I not done that, I'm not sure my girl would've survived.