Thank you very much for the additional information. It certainly was very helpful.
The fact that the headaches typically come in the morning upon waking and mostly on school days does indicate that it is probably stress related.
You mention that he is being seen by a psychologist - is this like regular therapy? And if so is the psychologist using any particular modality?
The way I see it - there are very clear worries/fears/obstacles in his mind that are so hard to face and deal with that he represses them to the point where they come out psychosomatically as physical symptoms. Therefore to solve the problem two things are very important - 1) teaching him the skills/techniques to address those particular fears whether it is peer pressure or bullying, anything at all that worries him 2) provide him with ways to externalize his fears/anxieties
whether it is by verbalizing it, working out or maintaining a journal 3) uncover the beliefs that currently hold him back from dealing with his worries more assertively (an example of a limiting belief could be - "I do not have the skills to deal with xyz" ) which then translates into his receding from facing that challenge.
In order to address the 1-3 points I listed above, a cognitive behavioral therapist will be best able to help. Cognitive behavioral therapy is goal driven and action oriented and your son should typically start seeing results within a few weeks. In order to locate a therapist who specializes in CBT you can click here
and search by zip code then when the results show up on the left hand bar you'll see the option to search by orientation and under that CBT. Click on that and you'll have the list of practicing therapists who specialize in CBT.
I hope this was helpful. Please do let me know if you have additional questions/thoughts/reactions.