HELP: Stitches came out?!?

I'm 3 weeks postpartum and had a first degree tear that required stitches. My OB said they'd come out on their own so I took that to mean they were dissolving stitches but when I went to the bathroom, I found a small piece of string on the toilet paper and I'm sure it's not from any clothing I own so I'm 99% positive that it's my stitches. Is this normal?? Should I call my OB? Note that there was no bleeding and no pain in the area 😕