maybe check out TMJ dysfunction.
I went to several doctors, a couple neurologists, ENT doctor, had allergy tests, did acupuncture, massage therapy, Craniosacral therapy, chiropractor, dentists, naturopathic, changed diet completely, damn near everything but a witch doctor. Spent close to $20,000 out of pocket in 1 year on various treatments, tests, MRI's, medication, etc, (and I have good insurance). After all that I was finally diagnosed with TMJ dysfunction and the treatment I'm doing now is helping a bit (which is better than anything else so far).
I've had literally the worst headache of my life almost every day for 1 year. It's finally down to a more manageable situation (although I still have daily migraines and am in pain for about 75% of my day).