+200 on checking the breathing test. Another thing to chip in, do you have allergies of any sort? I used to get really breathless while cycling, walking, running or climbing up the stairs. It was only this year that I started getting the congested, irritated feeling somewhere in my chest and having difficulty drawing a full breath. My doctor's verdict was that my allergies are bad and frequent enough to make me vulnerable to asthma.
If nothing is wrong health-wise, it could be that you need to build aerobic capacity. Long steady effort rides with an easy recovery ride the next day could help.
"My school is the doubt in your eyes." - Tito Mukhopadhyay