Hi welcome to HCM.
In case of asthma
it is not necessary to exert your self to feel breathlessness. It occurs even at rest and is triggered by house dust or pollens in the air. If you have breathlessness only after coming home then it is unlikely to be asthma. You need to check your hemoglobin
level in the blood or any heart problem. Best is to consult a physician to get a complete examination done to ascertain the cause of breathlessness.