If your doctor has said that shortness of breath
is not because of your heart then you have to rule out COPD which is a common cause of shortness of breath especially in smokers. You should get a PFT and a chest x ray
done which will help in establishing the diagnosis. In the meanwhile you may take inhalers like seroflo
and tiova 2 puffs twice a day and tablet doxyphyllin400
twice a day.