this really sounds like environmental allergies
atopica is a drug being used for this and if atopica and temaril p work then it is not food allergy but many allergy dogs have a combination of allergies -- flea, food and environmental
you are lucky if food but it is only 10% of allergy issues. Do you have winter where you are? if your dog stops itching in winter then you know it is environmental -- prob is most dogs have mold allergy too which starts up in winter months --- the book allergy solution for dogs is an excellent easy read and it is by dr shawn messonier and he has a yahoo group as well that i am on