What Causes Pain Under Armpit And Left Side Of Chest?

i have not been feeling well for about a year and a half. Doctors can't find anything. I have a pain under my left armpit and on the left side of my chest from time to time. I was working out 3 days a week and playing basketball 2 days a week. I have had to stop it all. I have 3 stress test and 2 nuclear test and they have told me it is not my heart. Just not sure what to do