diaper rash- when to go to ped's office?

How bad can it be to still treat at home vs you'd want your ped to look? Baby girl has some pretty good size raw spots that won't heal....the diaper cream won't stick to them and it's super hard to get the poop off her butt and avoid these spots when she poops. We're leaving her bare butt as much as we can. She keeps pooping when she's sleeping at night so we don't know about it until she wakes up :(.