What causes frequent urination in a child?

Hi doctor,

My question is for a child: 6 years, female, 48.5 pounds. Symptoms: has frequent urination during day 5 minutes- 1 hour starting from about a month ago, if she wakes up at night she will go pee; she is diagnosed with pollakiuria and cystitis. The symptoms started with gradually more and more frequent urination. She has no pain when urinating or during a medical examination of the lower/higher abdomen. Stool is normal consistency with a frequency of one to three days. Other medical condition include, general condition is okay, she has constant small pain around the belly button since she was little, unconnected to what she eats, time of the day or stool/pee; she is used to ignore it; she has a light form of vulvitis meaning it gets red and starts scratching so in order to fix this we use a dermatologic creme recommended by a dermatologist: Cicalfate; before bed each day, we wash her and use the creme; and the skin returns to a normal aspect if we keep using the creme; we tried other cremes as well, mostly they work but if we stop the treatment it starts inflammation again. There is no kind of liquid or secretion from vagina.