Bad 'sinus' headache but no cold, no blockage - what is it?

[Prunnhilda]

My sinuses really hurt, above my jaw and behind my eyes

I've had this before, and it comes on in the afternoon/evening, every day for a good long while (six weeks or so, at a guess). I used to get it as a student, then didn't have it for years, now I get it three or four times a year.

Because there's no sign of infection, I'm guessing it isn't sinusitis. What on earth could it be?

Sinusitis can occur without infection being present. I get this quite often and have a steroid nasal spray to keep things manageable and the pain at bay. Ask your GP for treatment.

Thanks. I am beginning to wonder if it's an allergy to....oh my lord...chocolate.
It's come on early today, and seemed to the minute i had one of the leftover easter chocs. Bugger.