Toddler has had rash for 2 months on and off

My daughter is 3.5 and has always had super sensitive skin. As a baby she was constantly getting rashes on her butt even being changed immediately and we went through so many diaper brands and nothing work.

Well she’s potty trained now and only wears pull ups at nap and bedtime. She occasionally has poop accidents but I change her immediately. Well 2 months ago she started preschool and we were having some accident because she was nervous to ask to go to the bathroom. She developed a yeast infection rash during that time. She goes to a headstart program so they are allowed to help them wipe and stuff but idk if they are or not.

She hasn’t had accidents in awhile but we are having the hardest time getting the rash gone. The rash will go away and we’ll continue using the yeast cream days after it’s gone like the dr told us and then it always comes back like 3-5 days later.

We’ve gone back to the doctor four times for this. We just went. I used the cream and the rash went away so I continued using the cream. While still using the cream 3x a day, my daughter had a poop accident and it came back 10x worse. It’s absolutely horrible. I feel so bad for her nothing they’ve advised us working.

We changed pull up brands, changed to a sensitive soap, started washing her crotch with just water and a rag, we used the Nystatin yeast cream, triple antibiotic ointment, and hydrocortisone all at once and it went away but came back a week later.

I’m at a loss. The doctor is too. They just keep sending in more nystatin but it’s not working.

Any tips? I’m desperate.