My daughter got a really bad rash within the first week of being born.. I was told it was bc she’s…

My daughter got a really bad rash within the first week of being born.. I was told it was bc she’s on formula and it’s totally normal.. she’s 2 weeks old and I’ve tried all kinds of different things to help it.. corn starch helped the most but she has 2 blister looking spots on her butt that is not going away at all.. I’ve tried the cream the doctor recommended and nothing is helping them.. I let her lay naked during the day to air it out to see if that helps and it doesn’t.. Ive changed her diapers and wipes to see if that was the problem and still nothing.. could it be her formula or is this normal and will go away in time? Seems like I’m at a dead end and don’t know where to go from here to help her and it’s so annoying I can’t get rid of it.. 😔😔