Thank you for all your suggestions--I think we found the culprit.

Andrew has been eating a yogurt a day, cheese curds, and string cheese (not every day, but enough). Two of my brothers are lactose-intolerant. It's a very good possibility this is the cause of Mr. Andrew's loose stools. We're starting a dairy elimination diet to see if it helps. If it does get better, then that's probably what it is. He can get his calcium from his Gummy Vites, but this nasty peanut butter poop has got to go! He has 3-4 loads a day and his little bum is red.

I'm wondering now if his reflux he had from newborn to 7 months was maybe related to the dairy in my diet. :(

If he is; indeed, lactose intolerant, hopefully it's not a lifelong thing. I'd hate to think a kid in Wisconsin has to grow up without the wonderfulness of WI cheese curds!