I agree with Annica and Amy above. If it is yeast, a cream won't do any good. Yeast is systemic which means if it is in her vaginal area, her body is eaten up with it. The only way to rid her body is a probiotic and taking away the sugar. Sugar feeds yeast and it is in so much that we eat today, even baby formula. Unless you get rid of it completely, it will just keep coming back. (Which you said every time you change something you get a new rash.)Prescriptions just help in the vaginal canal and it will keep coming back if it is yeast.
A&D also has so much petroleum in it that it clogs the pores and can actually make it worse and spread. I also agree with Annica about the Soy. I wish I had known when my girls were little as I gave them soy as well. There is too much phytoestrogens for little ones. It can cause problems down the road. (Also most manufacturers add sugar to the soy to make it taste better.) I thought my daughter was lactose intolerant for the longest time and then realized that she was just reacting to the chemicals in the milk. She can drink organic cow's milk just fine.
I use Melaleuca products that have a wonderful probiotic/prebiotic that is okay for babies and also the melaleuca oil that Melaleuca carries is not caustic (T36-C5) so would help on her bumps whether it is yeast or fungus like Jock itch. There is also a product called Tough and Tender that can be used in a bath. (My 15 year old has yeast occasionally and she sits in a T&T bath and it is soothing) If you go to the health food store, the higher the T number and the lower the C number is the better. Melaleuca also carries T40-C3. Make sure you ask about the amount your child should have by age and weight....
I hope this helps. If you would like to know more please let me know..