Mary-
First things first, you really want to find a practitioner to help. We can offer opinions and advice on what has or has not worked for us, but we are not qualified to give you any sort of medical advice.
There are several avenues to explore: including a homeopath, allergist, DAN! doctor, and dietician. But first, a detailed history (parent report) should be prepared so your practitioner will have an idea where to begin.
Now, what worked for us was to have extensive allergy testing done. My daughter is much improved with the use of desensitizing shots,a rotation diet and appropriate supplements (including fish oil and calcium). A book to check out would be Is This Your Child? by Doris Rapp.
Here's some info on a rotational diet through Great Smokies Diagnostic Labs. It's not the exact diet we follow, but is similar:
http://www.gsdl.com/home/assessments/allergy/TrueReliefGuide.pdf
As for foods, we use whole foods as much as possible. "Hidden" ingredients in prepared foods seem to be a problem. So we cook from scratch. You need to read every label. Example: most 100% juices are in fact juice, but they are a blend of juices. Apple juice is often used as a base for other flavors. Also, do your best to avoid food coloring, many medications contain them. I always opt for dye-free when given the opportunity.
Good luck! Keep us updated.
-TM
