What to do about sharp pain on the left breast when i breathe or sometimes it just hurt?

Costal;pleura: Costochondritis may be caused by trauma, such as bumping the rib cage; as a result of a viral infection; or as part of an inflammatory disease process. Usually the cause is unknown; pleurisy is inflammation of the lining of the lungs and chest (the pleura) that leads to chest pain (usually sharp) when you take a breath or cough.

Mostly time: You could try binding/wrapping your chest but your options are limited. Obviously you can't stop breathing!