RAST testing is only a screen; it is not 100% accurate.  Food skin prick tests
are more reliable, but even those don't necessarily show all allergies.  Plus,
food allergy skin testing can have up to a 50% false positive rate.  Some food
allergies are not IgE mediated (meaning that the antibodies which react on
skin tests are not involved in the allergy).  But in your son's case it may
still be worth a try because it can give you some additional information to
try dietary modifications.  The way they do them is really not paiful if it is
done properly.  My son had them done at 1 1/2 years of age and again at 6
years of age and there really wasn't much to it and no tears.

If you haven't seen a board certified pediatric allergist I would do so with
your child.  Sometimes family docs and pediatricians try to handle cases that
are way out of their league.