What Causes Red Itchy Rash On Vagina Of A 18 Month Old Girl Child?

My eighteen month old daughter has a red itchy rash on her vagina spreading to the inside of her thighs. It s been there for over two weeks. We recently changed diaper brands, could this be it? Also this morning there was a bit of light orange discharge when changing her. Is this just diaper rash or some kind of infection?