Have you ruled out dysautonomia? It refers to a disorder of autonomic nervous system (ANS) function. Most physicians view dysautonomia in terms of failure of the sympathetic or parasympathetic components of the ANS, but dysautonomia involving excessive ANS activities also can occur.
I know a family who have had an 8-year-old daughter misdiagnosed first with depression and then with bipolar disorder only to be later correctly diagnosed this past year at the age of 12 with dysautonomia caused by Postural Orthostatic Tachycardia Syndrome (POTS). The family and the little girl have gone through the wringer and are now trying to deal with the physical issues that cause the mental symptoms from a tough starting point after wasted years.
These two articles talk about two boys with POTS who are older (one boy's problems started when he was 12 the other when he was 13) but dysautonomia knows no age limits.
See "Ailment Can Steal Youth From the Young" New York Times, Oct 17, 2011 www.nytimes.com/2011/10/18/health/18brody.html
and "Migraines, Memory Loss: Was it all in his Head?"
http://www.washingtonpost.com/wp-dyn/content/article/2010/02/12/AR2010021204444.html