Is this a Yeast Diaper rash? HELP

Mac

My poor babygirl has this awful rash (I think it’s a rash) on her bum. She is 3 months old. Can anyone tell me what this is? Her Dr’s office is closed today and it looks so painful :( It kind of looks like blisters or something. I’m a FTM so I don’t know very much. BTW idk if this matters but this is between her legs, so not on the outside of her bum