12 month old has chronic genital itching for last 3 months my daughter had a yeast infection early sept 2011 the dr prescribed pediaderm diaper defense with nystatin... it did nothing so then he told me to put hydrocortisone to calm it down and prescribed

Rashes : Rashes are difficult to diagnose without actually seeing them. With everything that you've tried, i think at this point it's time to see a pediatric skin specialist (dermatologist). Call you doctor and ask for a suggestion of someone they know and like in your area. Good luck!

Contact dermatitis: It might be a contact dermatitis. I would bring her to a dermatologist for further evaluation and consideration of a very basic patch test.