When I first read this I instantly thought parasite. However I think we should try treating for an impaction before trying parasite for many of them
antibiotics are very hard on a bearded dragon's system. Have you felt the right side of his belly? Gently rub your finger up along his leg down to his
vent, or where he defecates, to see if you feel something hard. Sometimes depending where the impaction is, how big it is, if it is starting to break
down and whatnot you can feel it.
Another quick question, is he eating well? Having a loss of appetite can be a sign of an impaction.
If you would like to try treating the impaction to see what happens, if thats what he has, then give only soft foods. You can get veggie, and chicken
baby food, mix them, or have them eat them seperate doesn't matter much. Then warm it up a little, and try giving it to him. This is what I had to
do once for my baby. You can also add a very little bit of olive oil and that will help him.
Poor guy, I hope he gets feeling better!