The reason why your son could have food "allergies" - whether to dairy or other - is explained in my book CURING food allergies . You should be able to get it free out of your library.
Chances are - and it should be relatively easy to eliminate or prove this - your son's body temperature is involved. Read the book, which has very original information on the subject, and you will get an even deeper insight into the problem!
Best of luck.
Alan Hunter Ph.D.(A.M.)
Author: Curing food allergies and Common Illnesses