ok, not defending the OP specifically but I can attest to such a situation and no doctor being able to diagnose the problem.
I, myself, had similar problems and still have not actually been diagnosed with any true illness (over 35 years of history). I work very hard to avoid being diagnosed with a "syndrome" as that is not a true diagnosis as it is finding a name to apply to the cumulative symptoms presented. Once a syndrome is attached, doctors tend to stop looking for what is causing the problems.
While attaching a name to the problem might give the OP some relief as to the school situation, it does nothing to actually help her son.
The medical pro's simply do not have the answers to many of life's problems...yet. Until such time they do, my, and the OP's situation are what we have.
So, if the OP is not being buffaloed by her child, she needs to avail herself of the assistance available to allow her child to continue his education. I think that has been covered by others already.