I have 2 daughters ages 4 and 21 months. Well within the past week or so, everytime I give my daughters a bath, my 21 month old stands up holding her genetalia saying OWIE and crying.

She doesnt appear to have a rash or anything. Could this be a yeast infection? Bathtime is the only time that this seems to bother her, too. She wont even sit in the water now without crying, when she used to enjoy her baths. What could be wrong?
TIA