My dog has a similar issue, but we found out he is allergic to soy, because we gave him our daughter's left over bottle when she was a baby and he developed an allergy. Also, he cannot have chicken at all! the neighbors keep giving him those cheap dog bone treats so he keeps breaking out.
We have used Sulfadene and it seems to help with the itching and he doesn't want to lick it since it tastes icky, so he doesn't like it either.
I would put him on a good grain free food that is chicken free also like Royal Canaan or Canidae or even Blue Diamond (I think). Or, I got a good one at costco that was reasonably priced and safe for our doggy.
My mom works at a high end pet store, and she says that corn, soy, and chicken are the most common allergens in pet food today.