Hi! Many thanks for your question on eHealth forum!
Shortness of breath or inability to take a breath is medically called dyspnea. The problem can be either in heart or lung or due to anemia. Over exercising can also be a cause for breathlessness. At times empty stomach or drinking lots of water before exercising can also cause breathlessness. If you have a chest discomfort then, angina, heart attack and pulmonary embolism should be ruled out. If there is wheezing, asthma is likely. If there is cough, chronic obstructive disease or asbestos, silica etc pollution as the cause is likely.
Other causes are mitral valve problems, pulmonary hypertension, anemia, hyperventilation syndrome or psychological factors. A detailed and comprehensive investigation will be required including EKG, Chest X-ray, blood test for anemia, maybe CT scan of chest, BP recording etc. Please consult a doctor in a walk in clinic or go to the ER and discuss this with a doctor there.
Hope this helps. Take care!