Im 21, Female And I Get Really Bad Chest Pains

Im 21, female and I get really bad chest pains on the left and it seems to happen once a month. It lasts a whole day and night and is absolutely intolerable but it goes away the next morning. This has been happening for more than 2 years now. I also have sharp pains on the left of my left breast, this usually goes away in a week or two but when it does start hurting you can tell the nerves or something are inflamed. Not sure if its related. I went to the doctor when the chest pains first started but i couldnt tell where exactly the pain was coming from so the dr just told me to take some heartburn medicine which did not work. Im sure this isnt fatal but even once a month with this pain is really annoying. To be clear this has never occured during my time of the month, rather more often near the middle of the month. What could this be and how can i stop it?