He is young and there is no need for him to attend school. Is it a good idea to attend? Yes. But it is not mandatory, particularly if he doesn't seem to be ready yet.
forget about school for now if possible as he should be with u and daddy or grand parents etc.
ALSO there is always the possibility that he has good reason not to want to go to school and that would be your responsibility to learn
as to his health; try this; go to vitamin store and buy super high culture count probiotics and then from grocery store some plain yogurt and put a couple capsules (pull apart and mix in yogurt) and add any fruit in season or what he likes , NO SUGAR , maybe 1/2 pac of artificial sugar
water only (tap is best) never buy purified , if store water get spring water is possible
AS TO HIS ALLERGIES u did not say what they r, but allergy shots even for a very short period of time can be 10 x better than u imagine (it is a homeopathy method)
and any allergy u can control like pets; get rid of those