I'm not a doctor - but if there's pain in that area - I would at the very least (if it were myself) place an emergency call into a family doctor and see what their input is.
Hi Wendy, Has he been doing any heavy lifting or weight training, as this just sounds like a strain, he needs to just relax take it easy for a couple of weeks why it gets better, but just keep away from heavy weights or heavy lifting, even when he thinks he better, because if he gets straight into it, it could just happen again.
Good Luck