I've had that happen too. Once after lap surgery - one incision got all swollen and pussy like a pimple and when it popped I could see the stitch so I pulled it out and it healed fine after that, but left a big scar. Second time was after having DD1 and I tore. again got a pussy pimple like lump - squeezed it and the stitch came out enough to pull out. They were only ever short though, not like what you pulled out. I think for some people it's just normal. If it stays infected then see your Dr for some abx.