What Could A String Hanging Out Of Vagina Be?

I just gave birth almost three weeks ago and I had to have stitches, so when I went to the restroom and I went to wipe I noticed a string hanging out my vagina, I tugged on in gently, and it felt as if it was connected to something. It doesn't hurt or anything, but I still wanted to know is it just a stitch? if not what is it and should I call my doctor?