I don't know if this is the case or anything but my grandma and aunt's poodles got a hold of some deer poop outside (for some reason they really have a nose for it) and that made them throw up and have the runs. The vet told them to feed the pups skinless chicken boiled and rice (the rice helps with the runs). They got better after that and of course they were dehydrated but it sounds like you are doing well with that part of it. I hope he feels better!!!