I have had my beardie for 6 months or more and 3 days ago I went to hold him and he was skinnier and wrinkly on his sides. He eats really well, his name is Chub Chub for a reason haha. But I don't know what else could be wrong. I give him bath once or twice a week and I feed him crickets, meal worms and his veggies.
You can try by giving some oral fluids too, via a plastic dropper or syringe if he appears more dehydrated or wrinkly. Could he be going to shed soon? Sometimes their skin gets more wrinkled in appearance prior to a shed, too. You can increase his baths too if you would like.
Does he eat greens/veggies pretty well on a regular basis also?