What Causes Pain Under Breasts Causing Shortness Of Breath?

Im a healthy 18 yr old female 154lbs. & 5'3. I have been suffering from pain under my breast for several years. I have had to other female friends my age that have had this too. At random times I fell like I'm being stabbed in the chest. I t hurts to breathe in and even breath in deep. I try to take short breaths until the pain goes away.The pain lasts from a few minutes to sometimes a day. The pain also varies sometimes its just a slight pain sometimes its so awful I start to cry. Please help me out if you can. Thank you