I'm so sorry to read of your son's distress. I'm a Volunteer Mentor with Mayo Connect and not a medical professional. I can't offer medical diagnosis or medical solutions, but I do offer my experience, knowledge, and support.
At this point from your description, I'm very concerned about your son's situation. If at all possible, please obtain an immediate appointment with Mayo Clinic for a complete workup and diagnosis. They are great diagnosticians. It sounds like your son needs immediate help. Look at the top of your screen on the right and you will find, REQUEST APPOINTMENT. His doctors can also help by requesting an immediate appointment at Mayo Clinic. There are 3 clinics, in Rochester, MN, Jacksonville, FL, and Scottsdale, AZ. Try at the one closest to you, but I recommend you go to the one that can get him in the soonest.
I can imagine your distress about his loss of health over 3 years. Do you know, or have you asked if he's had an aids/hiv test? If he hasn't, that might be a step to take before his appointment with Mayo Clinic. Not that I think he has it, but it will need to be ruled out. I hope the best for you and your son, and will hold you both in love and light.