Painful Urination During Period Painful Urination Tested Negative For Bladder Infection Or Any Other Vaginal Infection. What Could It Be?

Painful urination tested negative for bladder infection or any other vaginal infection. What could it be? - painful urination during period

I sometimes painful urination for one week. I went to the doctor said it was a bladder infection and were negative. The doctor has a vaginal smear were negative. All suggestions of what might happen?