I recently had a horrible yeast infection rash which I think is either the same or similar to diaper rash. I used ZeasorbAF powder. It took 3 days for the rash to disappear.
I thought about it. I had been taking an overnight train. I was a little sweaty during the trip. I had been wearing mostly synthetic materials.
Use only cotton diapers. Change all lotions, soaps that you are using. Also, I an prone to yeast which flares up when I eat products containing yeast. You may want to try changing what you feed your child. If the child is in a warm, moist environment, change the environment to cooler and dry.
In the past, I went to dermatologists for this, but it did not help. My internist gave me pills to counter the yeast.
Hope this helps.