When my daughter was 9, she started falling apart mentally and physically. She had a years long migraine, tremor, muscle twitching, POTS, cognitive issues, and more. There was a time when she could barely carry on a conversation, her cognitive problems were so bad. I was afraid she was headed for the psychiatric hospital for a long term stay. Instead, our therapist encouraged me to treat it as physical and to believe her when she said she felt sick.
Regular doctors were mostly unable and to a certain extent, maybe not very interested in helping her. I think they mostly thought it was a psychiatric issue. At one point, I was told that she had a mood disorder and needed more exercise as the answer. She could barely walk at the time!
Long story short, she is much, much better today at 15. She plays sports and goes to school. Her headache is gone. We did not treat her as a mental case but found doctors who treated her medically. We had to go to out of mainstream doctors. If your son has medical problems as well as psychiatric problems, I would encourage you to look for answers to those before thinking the whole thing is mental.
In my experience, physical problems have been the cause of mental problems and not the other way around.