Hi, I'm so sorry you and Vegas are going through this. I agree with others comments about it being a traction or upset stomach from the antibiotics, if you are sure he hasn't eaten anything, or gotten into anything. I would hold off on giving him any food, to let his stomach rest, but offer him water. I heard you can give Pedialyte as well to replace fluids. Try a light breakfast of maybe half his usual amount, and see if he keeps it down. If he does, then feed him a bland diet in the evening, and maybe for the next couple of days. Have you checked to see if he has a fever? If Vegas continues to vomit after today, or if he has a fever, then I would take him to the vet, to have him checked out. I hope he feels better soon, sending hugs, love and prayers for you and Vegas. Please keep us posted on how he's doing.