I was going to suggest the same as Lottie, see if any migraine medication helps. I find Migraleve brilliant on mine.
The more prolongued ones I've had were related to going on Dianette (contraceptive pill), starting to take my arthritis meds and changing to artificial sweetners. Is there anything which could have set it off?
A colleague was complaining of a similar grumbling continuing headache. Someone suggested trying antihistimines and she said he helped a lot so figured it was something she had a reaction to. So it might help but finding any trigger would be best to be able to avoid it.