If the pain started after bouncing a barbell off of your chest there is a very good chance that the pain you are experiencing is related to damage to the sternum, cartilage of the costo-sternal joint, a rib, a muscle or any combination of the above. I would recommend getting checked by a doctor who specialized in the musculo-skeletal system - your friendly neighborhood chiropractor.
He or she should be able to determine what is going on with your thoracic cage.
-scott