I have recently started running after a 20 year absence. I have chronic allergy and sinus problems which do not hinder my 4 mile runs. Recently, I noticed I am far less winded running after I take a 12 hour antihistamine/decongestant(Allegra-D) before running. In fact, I probably could run quite a bit more before I am as winded as I am without taking the meds.
What could be causing this?