Hello and hope you are doing well.
Asthma can be detected by spirometry. There is an entity called exercise induced Asthma, here as the person starts exercise, the changes in the environmental air breathed in trigger an attack of asthma, causing cough and breathlessness. Have yourself evaluated for the same. This can be detected by a spirometry test.
Hope this helped and do keep us posted.
Do you suffer from nasal congestion, a common allergy center of action. I do and it makes me feel I have trouble breathing, but I in fact just have trouble breathing through my nose.
Whatever, has anything in you environment changed a couple of years go? Think about it, work place, home, travel, diet... there may be some allergy stimulant source you can identify by matching symptoms with something external.
Were you ever a smoker? Than can cause damage to the lungs that make breathing difficult. In general I think that happens only after many years as a smoker - or I now hear, being exposed to other smokers.