Any suggestions for the cause of a 3 day headache?

In the last few months I've been having these really painful headaches that last around an average of 3 days. Sometimes more but never usually less. I've always gotten them since I was around 5 or 6 but it wasn't that often and now I'm getting once a month and sometimes twice. They hurt so bad. I've had one now since Saturday. It effects everything I do. I can't eat because it makes it even worse and heat makes it unbearable. I'm thinking maybe Migraines? Anybody know of any other problem it could be? Any symptoms that include headaches? I've looked online but haven't quite found anything. I don't know if I'm allergic to anything or not and pain reliever does not help at all. Thanks.