Baby poop (picture)

My daughter has been having some diarrhea for the past few days. Starting yesterday it's burning her skin. My husband heard her poop and changed the diaper right then and there and her butt was already bright red. She hasn't pooped overnight since she was 2 months old. Last night she woke screaming her lungs out at 1:15. When we got her she had pooped and it literally burned her skin. Cleaned her up put butt paste calmed her down with snuggles she went back to sleep and woke up this morning at 7 with another poop burning her. What could this be? Lucky our pediatrician is open Sundays but they don't open for another few hours. Just curious what you guys think it could be?

She also just pooped again and there was a little blood. Now I'm getting nervous.