Medical question: Help! what could this be?

I was having stomach pain all yesterday, and at about 2:00 a.m. I woke up to really sharp pains and i went to the bathroom and i took my tampon out and along came 2 big slivers of something. they were really bloody, they had vains, and It looked like meat. I am on my period, and have been on and off for quite a while now. I had a colonoscopy just 3 days ago, and dont know if this contributed to it, but, im not pregnant. I have a 10 month old son, and I broke my arm a few weeks ago and they did a pregnancy test before i got x-rays, and i got a birth control shot last week. so i know it wasnt a miscarriage. does anybody know what this could be?!