does it hurt to breath?
If you hold your breath during a lift it could be (though very rare) that you can irritate a spinal-rib joint (costovertebral) in the back, nerves can send pain around the rib to the front.
Also, lots of weightlifters I see injure their serratus muscle during (usually) flat bench press because they don't use this muscle to stabilize their scapula during the lift.
get checked out by your chiropractor.
