TMI. Miscarriage ??

I'm not sure what it is. I was  sexually active while off my pills almost 2 months ago, and I started taking my pills again about 2 weeks after that. I didn't get my period the week I was supposed to and I figured I might be pregnant but today I started bleeding and having a lot of tissue like stuff come out. Is this just uterus lining, could it be a possible miscarriage ?? I've had a lot of this stuff come out throughout the day. I've had blood clots during my period before but nothing like this.