I suddenly got an excruciating pain in my left breast, sharp like my muscle is being squeezed. deep breaths and moving certain ways bring it back. er?

Yes: Any excruciating pain of unknown cause has to be evaluated. It could all be muscle or costochondritis but i can't tell from your history. Women on contraceptive pills and who smoke are at higher risk for blood clots and there is a condition of lung collapse during periods (catamenial). From your short history, it is just impossible to make a diagnosis and you said severe or excruciating.