+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.