Less winded during running, antihistamines helping?

[FLrunner]

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?

[Suncbus]

Been having same problems. Breathing a full breath... Tried alavert 24 hr.. Worked!!!!  But only for like 15 minutes. :(   Wish I knew why?

[National Jewish]

It is likely that you have chronic allergic rhinitis and that the Allegra-D

[crystalfresh]

You and me both. :) See if the regular antihistamine helps the same with out the decongestant to know which part is helping you. :) I'm not a doctor so I can't give too much advise.