What was that?

Most of the time I don't have too much problem with allergies. But once in a while in the springtime something really gets me. I was feeling great Saturday at lunch. By Saturday evening my nose was acting very badly. I was pretty much wiped out yesterday with sinus misery, and this morning I'm much better. It almost has to be an allergy, but to what I don't know. For obvious reasons I'd like to avoid whatever it is.