Suggest Remedy For Constant Headache

I have had persistent, near daily, headaches for going on 4 years now. I have seen two local doctors and 4 speacialists, but no one can seem to help. They are now back after a period of normality and are back with a vengeance!! Please help!! Medication does little to nothing and I'd really like to find the root cause instead of just masking the pain.