yeast rash

my daughter had a rash that wouldn’t budge. it was red spots but not super irritated so i took her to the pediatrician where she said it was a yeast rash and prescribed nystatin. i was told to apply it 4 times daily until clear. ive applied it 5 times and now it’s blood red and raw and it wasnt before. when should you discontinue the use of nystatin on a babys diaper rash? also how would you know if your baby has an allergy to nystatin?

i want to add im calling her pediatrician in the morning