TMI Stitches After Birth

Crystal✌ • Mother of 2 girls and 1 stepson. Trying to conceive our first child together. TTC since May.
So I had to get stitches because of a tear after having my 3rd 10/13. When I went to my 6week check up I told my Dr I was still pretty sore inside and sex was painful. She said she might have stitched me a little snug inside. Meaning the actually muscles inside my vagina. I have never heard of this. What is the reasoning? I'm not complaining, sex is actually better now but I never asked her why I needed them inside as well...