Sorry to hear about the headaches, but very sympathetic, because I've suffered from migraines all my life, nearly, and knew that about the otc drugs because I went through the same thing. Everyone's different, of course, but what saved me - until I went through menopause - was Topamax. It's a drug usually given to people with epilepsy, but you take it at tiny doses. The list of side-effects is terrifying, except again you take such small doses that it doesn't have the same effect, but I did get tingling in my fingers and toes and memory holes and it made me very drowsy for the first week or so. But it cut my headaches by about 80 or 90%. When you have so few headaches, you can then really see what your other triggers are - for me, it's chocolate and smoked meat. Until you eliminate all other factors, like the rebound effect of OCT painkillers, you can't really do the preventative stuff (like avoiding chocolate...).

Anyway, good luck on your quest to be headache free! And Happy New Year!