When my husband is stressed he gets contractions and pain in his left lung side and I breath heavy he is only 24 years old what can it be?

Several things. This problem mandates a real-time (face-to-face) meeting with a doctor. A history has to be taken along with a examination as well as labs and other tests. Only after all this will your doctor be in a position to tell you what's wrong and what needs to be done to help you.
Possible asthma. Asthma is a common illness characterized by shortness of breath, wheezing, and chest pain. The symptoms are usually triggered by a cold, flu, environmental smoke, pollens, or exercise - but sometimes stress can trigger the symptoms too. A doctor can evaluate his symptoms and prescribe appropriate therapy.