In the meantime take pepto bismol for the diahrea. It tells you that on all the medical web sites.
Why in the heck hasn't he done something about this before now? There are many things that could be causing the pain and he needs to see the doc now - not in Oct. If he had stones, it's possible that one of them could have escaped into the bile duct and be causing problems. He could be having spasms of the common bile duct, or he could be experiencing problems with his pancreas due to an 'offensive' gallbladder that may have started at, before, or after surgery. There are so many things that could be causing the pain, that it's hard to even list them.
But he can't wait. Tell him now - not October.
Diarrhea is probably due to 'bile dumping.' He may not be able to process fats the way he did before surgery and he should be following a low fat diet. It may help.