Do I have seasonal allergies right now?

today I had a headache from pressure in my head. I took a decongestant and the pressure went away but I still felt a little congested. I got tired and lightheaded too and I took another decongestant and wasn't as tired but still lightheaded. could this be allergies? I usually get allergies in spring and fall. plus I think I already had allergies about a month ago as well