PF

I have always been under the impression that babies who are exclusively breastfed have poop/stool that is basically odorless. That was true for the first few weeks of our son's life, but within the last week his poop/stool has suddenly begun to smell somewhat sulfury. You can tell when he's poopy from several feet away. I did not think this was normal -- could this be a sign of a problem? He also seems gassier than usual, especially at night, and every time we change his diaper there is a smear of stool, even if he hasn't had a "real" bowel movement. He's also a little bit congested in the nose. Could he have a cold? Could it be something I'm eating? He has a well-baby check-up on Monday, so I'll ask his pediatrician, but was wondering what others' experiences were....