It is painful when i breath in on my left hand side under my lung. when i sneeze or cough i get a sharp pain. what could be the problem?

Chest pain: Unless you have a rib injury, very often such sharp, fleeting chest pains brought on by a deep breath or cough is due to a pinched intercostal nerve or muscle which runs between 2 ribs. These resolve on their own. However if you have a significant cough, pleurisy or pneumonia can also produce sharp chest pain. See your physician if symptoms persist or cough worsens.