I ended up not having to take him, but I think everyone was right about the anal glands. The next morning, while I was waiting to call the vet, we went out for a walk in the neighborhood and he pooped THREE times! He wasn't stopped up becuase he didn't strain or anything and I had checked his bottom already, so I don't know what THREE was all about, but after that we got home and he hasn't licked since!
