If his appetite isn't too good, it's a good ideal to take a poop sample to a reptile vet for a fecal just to make sure he doesn't have alot of parasites. Parasites can prevent growth in an otherwise healthy animal. Small crickets are much better to feed, as too large of a cricket can cause impaction and lower leg paralysis. Keep the crickets no bigger than the space between the dragon's eyes.
Feed as much crickets as the dragon can eat in a 5-10 period. If he still doesn't show much interest in eating crickets, try silkworms. These are healthy feeders with very soft bodies (they are basically catapillers) with a high calcium content as well as protein and water. Silkworms can also be fed as a stable insect instead of crickets. Superworms are good as well but not as a stable, as they tend to be much more fatty and do have a harder chitin. Other good insect feeders are several species of cockroaches (avoid the ones with very hard exoskeletons, discoids seem to be the best for bearded dragons and smaller lizards), butterworms, small hornworms (big green catapillers, just feed the smaller ones, as these worms can grow to over 4" in length, which is much to big for the size of dragon you have.) Just make sure to feed the hornworms the prepared chow, if they have been eating tomato plant leaves or tobacco leaves, the worms will be toxic to your dragon and other reptiles. Toxins come from tomato and tobacco leaves, not the chow specially prepared for the hornworms in the reptile industry.
You could also add a small amount of gateraid or unsweetened low fat fruit yogurt as an appetite stimulant. These help replace any missing electrolytes and beneficial gut flora. offer a small amount daily for a week could really make a difference in appetite, especially after any treatment for internal parasites. A product called Parazap is also said to be beneficial in helping good gut flora and stimilating appetite.
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PHLdyPayne