Why can't my doctors know where the air bubbles come from in my chest cavity?

Air bubble in chest : Pneumomediastinum or air in the chest can come from lungs, trachea or esophagus. It can happen from deep sniffing, drug abuse, and heavy exertion. I see a number of teenager with lot of air in the chest from unknown cause. Air can also come from root canal. Air bubbles can also mean infection. It may be sign of grave disease process or it may be totally benign requiring simple observation.

They can: Lung-trachea or esophagus those are the only air containing structures in the chest. Usually from blebs in lung, or following lung trauma or surgery is where one gets persistent pneumothorax or air leak. With some infections, the germs will generate gas bubbles but doubt that is the issue!