Two years of daily headaches and your doctor has only tried one, so far ineffective, medication? I'd say it's time to find a neurologist who specializes in headaches. There are lots of possible preventative medicines out there, and a good doctor would be methodically trying them with you to find out what works. The American Council for Headache Education and the National Headache Foundation (I think i've got the names right) have lists of member physicians, which is a good place to start if you don't know of any headache docs in your area.
Even a nonspecialist should be trying several meds with you. Unless you haven't been back since he first prescribed whatever it is you're on. You can read through this message board and other headache sites to get ideas of what other people are using and ask a good doctor if that would be an appropriate thing for you to try. Some meds that come to mind are Topamax, tricyclic antidepressants, beta blockers, tryptans, Neurontin, Lyrica -- the list goes on and on. All of these tend to have some side effects, but they affect different people differently. Headache medicine seems to be a lot of trial and error, unfortunately, which is why you need to find a doctor with whom you have good communication.