I Just Gave Birth 3 Weeks Ago, I Became Sexually

I just gave birth 3 weeks ago, I became sexually active about my second week of giving birth. I also had stitches, I didnt eally experience pain or anything.Yesterday I took a look & I noticed like a string coming out. Will my vagina go back to its size or since I didnt wait it stopped the healing process? Should I contact my doctor?