Is the vet certain that his tummy has healed? My pup had giardia and we were advised it can be tricky to clear it however first course of treatment sorted it.
Could it be possible that he is being fed too much as that can cause loose stools?
I have read your other post and see you're using beta puppy food, according to all about dog food website that is actaully worse quality than bakers and pedigree. I really don't understand 'breeders' that don't research the food they give to their pups.
I know you are keen on the raw but if my pup was on beta he/she would be getting moved to something else a lot better quality.
Before even considering changing his diet I would be making sure his tum is better first incase he has got worms or giardia etc