Hi Speedy G,
Have you tried Vicks Sinus spray? I would be lost without mine.
You say that you feel it may be sinus related but, disregard if you have, have you considered getting your eyesight tested? Bad eyesight can cause headaches.
I see from your profile that you are a student so I doubt you are flying in pressurised cabins but maybe dehydration could've been a factor. I know of many flyers (not just in pressurised A/C) that have complained of headaches bought on by this.
Hope this helps a little.
All the best, VFE.