Hiya,
Can you tell us what type and dose of antibiotic he's on?
The antibiotics often cause upset stomach. Don't be surprised if he has abnormal feces as well. Generally, you just have to stay the course and power through... It's good that you got him to the vet, I am sure the exposed bone hurt a lot and the antibiotics will keep him safe. As a Microbiologist, it's my duty to stress that using the complete course of antibiotics is very important, unless your beardie is in an extremely critical state because of them.
If you are extremely concerned about his appetite and energy, you can try feeding one of the "syringe" diets. ReptiBoost is popular, as is Critical Care. I've used both with my rescue animals, including a mostly blind leopard gecko who refused insects for years due to her injuries (She was on the liquid diet for 3 years before I received her 6 months ago. As of four months ago, I got her accepting meal worms, phoenix worms, and wax worms. She's now also willing to take crickets and dubia roaches when hand or tong fed as well!). For your situation, I would suggest the Reptiboost, as it is more readily available in most pet stores and comes in smaller packages (the size you would want while using it for a temporary diet) as well as with clear and complete instructions for bearded dragons in particular. Unlike Critical Care, where you need to do a lot of googling and cross referencing, Reptiboost comes with everything you need including the syringe.
Even if you do feed a liquid diet, I would not suggest force feeding him much. Give him a little time, I am fairly certain he'll recuperate just fine even without the liquid diet. You also might want to call your vet with your concerns, they might be able to ease your fears.
Out of curiosity, what is your set up otherwise? Now, of all times, it's especially important that everything be spot-on.
Good luck,
-Ellentomologist