In my unqualified opinion, you may be experiencing symptoms that give all the signs of asthma, but will simply go away.
Certainly getting fit, or fitter, will do nothing but good. While running, force the last creaking molecules of air out of your lungs and fill them fit to bust. ( work gradually up to this of course ) Most importantly, concentrate hard on thinking that this cold air going in is GOOD.
So many asthmatic type reactions are about the mind shutting systems down because of perceived danger. (This is a ‘hobby-horse' of mine, but is backed by some good science.)
When I wanted to go back to flying after a long break, my GP said, "Oh, I don't know...you had that asthma thing a while back." I told him how I had forced good clean air into the lower reaches of my lungs–sounding like a church organ on a thankfully deserted beach--and gradually got back to a top of the scale reading.
It has to be said, that whatever caused my sudden problem was very unpleasant.
You might even try running before the test so that the differential is not so great.
I know someone
who was excused from all sports at school, then drew a crowd round the old puffer machine in Pread St. cos of blowing the needle off the scale.