5 yr old girl. urinary frequency. no confirmed culture. blood work up done/ normal. what could be the cause?

Several issues: A 5yo without fever is less likely to have a uti, but may have irritation or stress induced frequency.Shampooing her hair or otherwise sitting in soapy water can leave a soap film on her genitals that leads to irritation. Some kids can go thru periods of frequent urination after observing a stressful event. A scary news video or perceived dangerous event can set this off for a month or so.