What can be the cause of a 4 year old crying that it hurts when she urinates?

Within the last week when she would go to the restroom, she would use the bathroom but then 2 or 3 minutes later have to go again. (I thought it was just that she was nosey and didn't want to miss anything, so she would not completely finish) but today (when all the doctors are closed around me for the weekend) she has been crying every time she goes to use the bathroom that it hurts. I ask her how does it feel and she just cries. I did have some diaper cream and tried that, I tried power but none of that seems to work. What should I do? What could be the cause of that? She is not a soda drinker and we are clean people, she bathes nightly..