Arlene,
There are so many different proteins in dairy products.  Casein is a big one.
 My 2 year old son is anaphylactic to dairy and so we strictly avoid ALL
dairy products. According to my pediatric allergist it's very hard to
determine exactly which or what specific protein is the culprit.  I
understand it can be done, but he believes for our situation that is not the
best route to go.  Try to eliminate all dairy for a while and see how that
goes and talk to the doc again.  If your still not satisfied maybe you should
get a second opinion.
best of luck,
Lisa