It might be worth considering the possibility that he is suffering from depression. The mental health profession is beginning to recognize that depression can begin at a much younger age than was previously believed, and the symptoms are often very different than those found in adults. In fact, they are often very much like what you have described in your son.

It might be difficult to find a mental health professional who can evaluate him adequately for depression because not all mental health professonals are in agreement yet about this. But it might be worth having a look around, or maybe read up on some of the more recent literature yourself. Sounds like something you want to take very seriously, though.

Good luck.