A headache behind one eye is a migraine headache. There are lots of triggers--not just chocolate. For my wife, smoked pork will cause one as will intense sunlight and a variety of other things.
I only had two migraine headaches in my life. The first came on suddenly, after I walked out of a dimly lit building and right into the bright sunlight. It came on instantly, and I was out of two. I had two soft drinks loaded with caffeine and the maximum dose of Advil I could take and made it home. The other started out as a normal headache, but continued for several days and turned into a migraine. There is no over the counter treatment that I know of, but there are medications, including injections that can offer immediate relief and pills which take a little longer but do not always work. You have to talk with your doctor. If you are getting them frequently, then the doctor may tell you that you cannot take any remedy for a period of time to make sure you are not suffering from rebound headaches. The bottom line is to see your doctor if you have a history of these headaches.