While it may be something harmless, ANY chest pain that persists, especially left sided chest pain that extends to other areas definitely needs to be checked out. I'd strongly suggest you make a trip to the local ER to rule out any serious.
Hope you feel better.
Well it very likely is your Spleen : http://en.wikipedia.org/wiki/Infectious_mononucleosis. Also, it could be scar tissue: breast Implants gll bladder surgery hysterectomy etc.. Read up on some of these areas good luck let me know what you find out. :)