Consider calling your local ER and speaking with the triage nurse and especially if you have neck stiffness, vomiting or nausea or a dilated pupil in one eye. It could be anything... I know there is a condition that is called temporal arteritis that can cause headaches as you describe.
Good luck !
I just started experiencing the same thing. Did you ever find out what it was?
I have the same problem, It started like a month ago, Did you find out what causes it?
A related discussion, head pain