It could be just your sinus's reaction to the weather changing. I known that the weather changes have caused a whole barrage of different feelings in my body (including my own sinus's) that have caused me alarm. Really however, I think you'll be fine. Take a hot shower, blow your nose, and all that stuff will just clear out (if it is the sinus).
If not it could also be a tension headache. (stress headache). That is one of the things I find beneficial to look up on google, because its a direct manifestation of anxiety, and usually on one side. What's more, its completely harmless. :)