Shortness of breath. Meters non stop.

I have dust allergy from past 3 years and slow its become asthma I got asthma attack 1 time  after that I asthma didn't come but after a month I feels shortness of breath.. Then I visit near by hospital he says my lungs is clean then I visit ENT he CT scan my nose and says no problem and from past 5 months mucus in my nose is very low as compare to past and sneezing is also very low..but I feels shortness of breath through out the day  now also while I typing this I feel shortness of breath.. And I check my hemoglobin its also normal..u didn't know what is the problems why I feels shortness of breath ...my mother says it is asthma but I didn't had chest tightness and sounds..and I can run 800 meters non stop..