G'day from one very mildly asthmatic person and a holder of a Class 1 medical and an ATPL.
Asthma is a condition that needs to be monitored and controlled to have the least amount on impact on your life.
If the doc didn't explain, take 2 readings of your peak flow per day. One in the morning (first thing ideally) and one in the evening. What the doc is looking for is a bench mark for yourself and to see if there's a 25% or greater difference between the readings. The morning one should be the worst.
Being active is good. You may find you'll need to take a puff before exercise.
My version is a cough and it took several trips to the docs and changing doctors to get it diagnosed.