It turned out to be thrush. We are both on a rather ineffective topical agent (Nystatin); the Nystatin had no apparent effect. Then, on Saturday, Jack and I started a probiotic.
Guess what? Sunday and Monday mornings were nearly gas attack free. He still had to toot a bit, and there were moments of discomfort -- but we're talking two or three 2-minute sessions instead of a 2 hour marathon of pain.
Good job, probiotic! Jack is much better, but I can tell that my infection is coming and going on an hourly basis. I'm not sure whether to request stronger treatment from my doctor or whether to keep up the natural remedies for a few more days.
I am so glad that Jack is feeling better. I seem to have had this infection from the start (I took antibiotics after birth), so I only wish we'd known about the thrush sooner. I plan to stay on a probiotic indefinitely. It seems that thrush can cause varying symptoms in the mother and infant -- he never had obvious signs of it, but I did. I'm thinking that a probiotic is a good idea regardless of how the two of us are feeling.
As a double bonus, Jack's gas pain does not appear to be related to my diet. Three cheers! Insulin-dependent gestational diabetes gave me enough food troubles during pregnancy -- it has been a relief to be able to eat normally again.