Could be... If you are young and having pain for more than a couple of days, without relation to physical activities, shortness of breath etc...Your symptoms could be simply from inflammation in the joints between breastbone and ribs (costochndritis). If you sit perfect still and don't have pain and when you move or breathe then have pain, it could be your chest wall/muscle spasm.. Check with your doc..
Go to the ER/Dr. Chest pain is a serious symptom. Depending on your age and history, a number of bad things could be happening. You need to be evaluated.
Anything. Could be a problem with skin, nerves, muscle, shoulder, lung, heart, or stomach. See your doctor for a more thorough history, physical exam and further evaluation.