What kind of pain is it? Does it feel like someone is stabbing you? Also, where does it hurt when you press down?
A few months ago I had a sharp pain in the left side of my chest. It came and went. When it came it only lasted about a minute, sometimes less. It hurt when I pressed down on the left side of my sternum and on the bone above my breast. The doctor told me that I had costocondritis, an inflammation of the cartiledge of the rib. Mine occurred because of some ackward lifting I was doing.
My advice would be to see a doctor about this. In the meantime a heating pad will help with the pain and ice will help the inflammation. But really you should see a doctor, just in case (I don't want to scare you, but you never know).
Feel better
Irish Princes