Help! My Pitt is chewing himself up!!!..........?

It could possibly be fleas. More likely though is allergies. Stop the brewers yeast as he may very well be allergic to it. Try a better food such as Canidae, Verus, or Timberwolf Orgaics. They have no grain fractions, no corn, no wheat, and no soy. Those are the major allegens and they are present in your dog's current food. Remember the foods I recommended require less to maintain the dog's weight so don't overfeed. Stop all treats (if you must give treats then dehydrate or bake some chicken livers and beef hearts but add NOTHING to them). No table scraps either until you find out what he is allergic to. It can take up to eight weeks for allergens to completely leave the dog's system. For now, ask the vet if you can give him some Benedryl and how much. You should have him in for a check-up anyway just to make sure nothing serious is going on. Also, bathe him with COOL water (warm and hot will actually irritate the skin more) and a CANINE shampoo specifically for allergies. After that, any time he comes in from outside, wipe him off completely with a damp cloth just in case there are allergens outside that are getting on his skin and bothering him. Make sure to get the paws and the skin inside the ears as well. Good luck with him.