I think your son will have to request a Jag officer visit as
@gtb1943 stated above.
I think parents might be able to send a letters to the commanders in his chain of command asking why the doctors orders were ignored. But I would not do so in a mean manner or even a threatening legal issues over it.
I would make a copy of the letter and show that you sent it to his chain of command. That could include the company commander, battalion commander, post commander. You might also want to send letters to Company First SGT, Battalion SGT Major, Post SGT Major and also SGT Major of the Army. Oddly enough the SGT Major of the Army might be the one that gets things done. We had issues of no AC in a few clusters of barracks at Fort Polk Louisiana in the summer for a few weeks. The Sgt Major of the Army happened to be visiting the post and took questions. One was about getting the AC fixed. Magically the issue was fixed in two days.
You might also want to contact your congressman that represents where you live to look into the issue. NOBODY START A POLITICAL rant in this thread. Whether you get any response is questionable but at least you can show that you sent requests of inquiry to multiple people.
I would be sure to ask your son if he wants you to do this though. Maybe he just wants to do his time and get out. Or maybe he has designs of continuing his military time and make a career out of it until retiring in which case he might not want the issue of any trouble hurting that.
With that said. He does need to take care of his health issues or he will not only not be able to continue a career in the military, but it may become an ongoing issue for him in his life outside the military and if he does have to leave the military due to health issues....He should be quick to get in with the Army VA medical services and also look into getting some kind of disability pay from the Army. They have various levels of disability rating and pay if you qualify.
Keep us updated.
Also, not sure if this site will help but could not hurt to look it over.
https://www.todaysmilitary.com/parents/support-parents