It sounds like seasonal allergies, because if it were asthma, there is no way you would be able to do any type of exercise, which would only make the condition worse.
Claritin has always been very helpful for me with my allergies, but only your physician can advise on what would be appropriate for you.
Good look, Judy
It's probably not asthma ... more likely something to do with your sinsues. The change in air pressure that you would find in travelling and climate changes also would bother your sinuses if they are plugged.
Try a decongestant and humity (sit in the bathroom with the shower running hot for 10-15 minutes). Look into a saline nasal rinse (one you can search for is neil-med) and try that to see if it helps to clear out the muscous.
If none of that works I would get a check-up with a ear, nose and throat doctor to see if there are polyps or a structural defect.
Also try to see if the stuffy is related to any allergies .... that can make it worse too.