Weird white substance in my vagina?

I have recently had unprotected sex, about 3 days ago. And I've had a regular period for a couple years now. But lately, my vagina has been acting weirdly, The skin around it burns, and it hurts a lot to wash it, so I decided to check it out. When I checked it out, there was a weird white substance inside which looked like a tampon string, although I have not put a tampon in.