Let me ask you a few questions.
Have you ever been diagnosed with asthma?
If so, do you take your peak flow reading every day?
If you have never been diagnosed with asthma, the first thing you have to do is to eliminate other possibilities.
I personally recommend you going to see a pulmonologist or allergist.
In addition to history taking, they would give you some tests, such as pulmonary
test, blood test, electrocardiogram or X-ray check etc.
To check your EIA(exercise induced asthma), peak flow reading before and after getting exercise might be helpful,
but remember that it is important to keep in close contact with your doctor.