The sensation of not getting enough air can be caused by a variety of conditions including
anxiety and panic disorder
obstruction to airflow in the bronchial tubes, such as asthma or bronchitis
a process that fills up air sacs in the lungs, such as pneumonia
fluid in or around the lungs
impaired movement of blood through the lungs so less oxygen gets picked up (for example, blood clots in the lungs)
a low red blood cell count (anemia) with low hemoglobin levels that can't carry enough oxygen to the body
a weak diaphragm and weak chest wall muscles that won't pull enough air into the lungs (muscle or nerve diseases).
Let's first address whether you have symptoms of an infection, such as bronchitis or pneumonia.