WHY didn't I figure this out sooner?
It's the shampoo I use in the shower! When I wash my hair, the shampoo runs down my whole body and (duh!) printed very clearly on the shampoo label is this:
FOR EXTRA VOLUME AND BODY.
No wonder I've been gaining weight! Well, I've gotten rid of that shampoo. I'm using Dawn dish soap instead. The label reads:
DISSOLVES FAT THAT IS OTHERWISE DIFFICULT TO REMOVE
If I don't answer the phone, I'll be in the shower.