First be sure that any food change is done gradually over 5 days or so. And as a side observation Blue Buffalo can be a bit rich and I have known of several instances where some puppies cannot make the change due to diarrhea. Although food allergies commonly are associated with skin conditions and itching, that is usually in dogs a year or more of age, itching from food allergy in a puppy his age is not likely. The first thing is to check and possibly clean his ears, take a look at the home demo video "Cleaning My Puppy's Ears" Also simple dryness is a common cause of itching in puppies transitioning to a new home and most often will resolve within a couple weeks.