I would say try a new food, it may not be appetizing to him. If that doesn't work, try another, then go see the vet. I would try Iams. My pug has been an Iams dog her whole life. Iams is one of the best foods because it is very bland and doesn't have "bad things" that is what my vet said. They have puppy food too! They have pro active, small/toy, senior, lamb and rice, etc. Iams also has treats, and bones. Do some research and see what you can find, like the best dog foods, or something to that effect! Good luck, and hope he likes it!!!!