K.W.
My 13 year old has not yet had the symptoms and she has not yet been to an OBYN. I suppose if she has her period already the OBYN is where you would start, otherwise I'd call her pediatrician to find out if it is time. If she is uncomfortable, a diagnosis might put you both at ease however Increasing yogurt usually stops a yest infection before it gets out of hand...so trying that first is less invasive.