Wow, I feel for you. Nobody should have to being going through that. I do tend to wonder what kind of doctors you have been seeing. Hopefully, a pediatric psychiatrist, and not just a pediatrician or a psychologist?
I am also the CL on the ADHD forum here -
http://www.medhelp.org/forums/ADD---ADHD/show/175
Many of the symptoms sound like ADHD, but I would assume that has been looked at? The next question would involve medications. Did they ever try either Prozac or Paxil with a stim med? That will many times lead to a very bad reaction down the line as the Prozac/Paxil will cause the stim meds to backup and overload the person. Anyway, what meds have been tried? When you said massive doses - I really got concerned. When you mentioned weight gain, I thought of Resperdal. Not a favorite medication of mine - has lots of side effects and a few law suits now on going. Many times, the meds are too much and causes more problems. It does take trial and error to get it right, but that takes good communication between the parents and the doctor. If the doc and you are not talking weekly, then its not happening.
He should (actually, must) have either an IEP or a 504 plan at school. You can't kick a kid out of a public school due to their medical problems.
I am not sure I can help - I mean you have talked to the experts. But, it does make me wonder what kind of docs you have been talking to? And what is the school system doing to help?
Opps, just reread your post. You have home schooled him since Dec. 2014? So you have been doing this all on your own? Have you visited the special ed schools in your public school system or had any interviews with the special education department? This definitely is an area you need to explore.