I Have A Pain On My Left Rib Cage Under

I have a pain on my left rib cage under my peck, it comes and goes, but is at its worst when I'm lying on my left side, I work out as a power lifter every day at the gym and am sure this is just a sore muscle of over use injury but being the area that is sore is above my heart I am a little stressed out by it, any thoughts?