vaginal pain in 3 1/2 year old

My 3 1/2 year old daughter has been complaining of vaginal pain, and had, what I thought were symptoms of a UTI. I took her to the PED yesterday and urine culture came back normal. PED felt around on her tummy and did a quick inspection of her vaginal area. He said it was a little red and he suspected she likely wasn't emptying her bladder all the  way during trips to the bathroom (one symptom she was having was returning to the potty right after she had already gone saying she had "'more" but not urinating that I could tell). He also told us to minimize playing in a soapy tub so as not to exascerbate the problem. I'm at a loss because she is still complaining of pain, tells me she "doesn't want to pee" and that her "butt and vagina hurt". I have been applying A&D ointment to her bottom, but I just hate it! Anyone else have a child that has gone thru something similar?