This happens to me twice a year, and no, it's not an allergy (unless you call being temperature sensitive an allergy). I've pinpointed it to the weather, and in particular, during the spring and fall when the weather starts being schizophrenic.
When the temperature drops or rises to a certain range, my sinuses decide to start plugging up. However, it only plugs up enough so I can't breathe properly, but not substantial enough to blow out. So I'm in a perpetual state of misery.
(You should feel doubly sorry for Hubby, who gets to listen to my constant whining.)