I am allergic to LOTS of stuff.....certain trees and grasses, ragweed, goldenrod, then there's melons, apples, carrots, celery (but if these foods are cooked, it's okay) and the sun gives me hives. And that's just the short list. Unfortunately, my seasonal allergies (especially ragweed) are so severe that most medications only provide marginal relief of symptoms. Usually it's prescription nasal sprays and Aerius for me, and yes I do get sinus headaches.
As others have said, your symptoms could be allergy related, but could also be from a change in pressure, a developing head cold or sinus infection, or even an irritation of your nasal passage that has caused inflammation. I would try a decongestant (someone mentioned sudafed) if the headache is persistent and is really bothering you. If it continues to bother you, you can always try an over the counter allergy medication and see if it alleviates your symptoms. Of course, if the problems continue without abatement or you develop any other symptoms such as dizzyness, fever, or coloured (green or yellow) nasal discharge, you should talk to a doctor or pharmacist, as these are indicative of an infection rather than an allergic irritation.
Good luck! I know exactly how annoying sinus pain can be.