It wouldn't be a pinched nerve if the pain is starting in his front. It could be anything from simply bad gas to his appendix. Sorry if what I say seems gross but I'm looking at this from a medical aspect (I used to work in a hospital). When was the last time he took a good number 2? If it's been a while he might want to consider sever gas or constipation. If this is the case, then tell him to drink plenty of water and he might want to increase his fiber intake. Or take a natural stool softener that you can get at Walmart. You didn't say what kind of test they ran but they should have ran a urine sample for kidney and bladder infection and a blood test for his appendix. And an ultra sound would look for gall stones and kidney stones. If all of this comes up with nothing then he might want to get his prostate checked since that is also located near the bladder.
I would definitely have him go back to his Dr since the pain is making it hard for him to breath and he is doubling over if it isn't a BM issue.
Good luck to both of you!!
S.