Diaper rash

So my daughter has had a little rash right in between her butt cheeks around her little butt hole for over a week now. We've tried butt paste, aquaohor, a & d, and some other ointment. We rinsed with warm water instead of using wipes, dried with a hair dryer, and let air dry one day without a diaper. I called the doctor and got nystatin and used for a few days and still there. It's small but it's pretty chapped in that area. She is EBF and poops a ton so I'm sure it's from that as she gets changed frequently. Help!!