@NYCmama
So many posters have given you great advice and things to consider. While I don’t have any experience in parenting a child with the challenges you face, I did experience the frustration of having to care for and entertain our D for long hours (entire evenings and weekends) while her father was at work (H is also a physician) or on overnight call. Much as I enjoyed being with her, my energy and creativity flagged and I have only one child.
In addition to having a tutor work with your son on his math and writing skills, you might also consider having a young adult come regularly a few hours each week and take over some of the interactive fun things you do with him now and be there just for him to chill out with. In the old days, this might be called a “babysitter.” 
It might be enough of a novelty for him to get him re-engaged in things that he is not interested in doing with you and there is always the new energy and different dynamics a young person brings. It would give you a break and free up time for you.
Perhaps you can get recommendations through your child’s counselors but this would strictly be a “fun” companion, not an occupational therapist type person.