Try him with a very small amount of live yoghurt. The antibiotics will have destroyed the bacteria in his gut including the ones required for digestion so they need topping up again.
Give it a good few hours and try him, this evening perhaps, with something very easy to digest such as white rice and fish and continue with the yoghurt in very small quantities for a day or two. As long as he has plenty of fluid it won't hurt him to go without food for a while.
I used to have a toy poodle called Brandy who regularly suffered from a gurgling tummy unfortunately and refused to eat anything, he was eventually diagnosed with collitis and the vet prescribed Buscopan for him which helped him a great deal, so I always kept some in the cupboard. I wish all the gluten free foods had been available at the time as I would have given those a try too. I have to say he still lived until he was nearly 14 years old. Hope this helps.