This is a common problem, this is your body telling you your doing something wrong, good idea looking for help.
I'm gonna throw a wild guess here and say you have a high bench press and focus on your bench press, and maybe military presses.
Basically, your deltoids are pulling your shoulders forward and taking on to much of the load. So rather then your pectoral muscles getting stimulated, your shoulders are being over stimulated and could possibly cause serious injury.
This could be a problem with your form, and also an under development of your rear deltoids. Basically what your going to want to do is do exercises that will bring your shoulders backwards.
(Ie, power clean, dead lift, bent over rows. and my favorite (Works lats and back shoulder muscles the dumbell pull over.)
Also, try moving your grip on the bar to a more comfortable position.
Last but not least, a simple test to see if your shoulders are rounded to far forward, is to just place your arms at your sides and let them go limp to natural position holding a pen in each hand. if the pens point in towards your body then shoulders are rounded forward. If pens point straight ahead, then shoulders are fine.