What Causes Burning Sensation In The Vagina?

I had sex with a guy over the weekend. We used a condom and I am on birth control. But I was still afraid because I forgot to take my birth control that day we had sex so I took the plan B pill. But I was stupid and took my birth control the same day I took the plan b pill. Now I have burning in my vaginal area, no discharge or smell. Why could this be?