Peeling Lump Below Baby Spine

My 7 week old daughter has a very deep indent with a little lump at the top of her buttcrack. Diaper lint, baby powder, and poop get stuck in there easily and I have to regularly clean it out with a q-tip. Hospital and pediatrician said not to worry about it, and she was seen a few days ago for a well visit where she was deemed okay again. Today I noticed the skin was peeling and when I wiped it clean, the indent was deeper than before, with the little bump now forming a point. It's really irritated and damp. I dried it as best I could and put a little breastmilk on it (I've seen other simple skin ailments of hers improve with this treatment). I'm not sure if she is too warm, diapers are too tight, if it is something serious, or if I'm being paranoid. Anyone experience this with their child?