sounds like a rib. Nothing will help it except time. I went to the dr when I cracked a rib and they essentially told me to go home and take it easy until it didn't hurt so much. (a waste of my time!) It really can be excruciatingly painful, it's not like muscles. what's worse is sometimes the rib moves AFTER the accident and that pain is even worse (probably because of muscle spasms) so be very kind and don't make him laugh too much for a few days. In two weeks he should be a lot better.