The advice given by previous posters is sound advice. I don't have anything to add except that as a mama, my heart breaks for you and your son. I think that PCS being so widely misunderstood and so hard to live with, is very sad for a child to have to deal with.
My son (only 9) recently got a concussion playing hockey. I'm a PCS sufferer so I've been very cautious with his return to school and he is still not cleared to play hockey. The thought of further damage to his developing brain makes my heart hammer in my chest...
I feel for you. You've come to the right place for answers and guidance.