I have burning sensation during and after urination. Why?

Hello doctor,

I had sex with my husband on the fourth day of my periods. One day while passing urine, in my vagina there was a burning sensation and it started paining in the abdomen area below the stomach on the right and left sides. After that on the next day, I had no pain. After that, again the next day, I had sex with my husband then again it started paining and burning during urination. In short, there is burning sensation while urinating and a persisting burning sensation after urination. Yesterday, we did not have sex but in the morning since 6 a.m. I am having a burning sensation in my vagina which is not at all getting fine. What can be the cause of this? And what should I do?

Please help.