miscarriage or uterus lining?

I was at work so I couldn't take a picture but when I used the bathroom, a clot (about the size of 4 peas) of stringy skin like grey-ish tissue came out. And I've had it happen a couple times over the last 2 weeks. I've been on my period for a month (because of the pill) I'm worried, could I possibly be having a miscarriage or is it just the lining of my uterus, I've never had any skin tissue like clots before. The fact of never had anything like it before makes me even more worried. What are the signs and symptoms of a miscarriage early on? (Edit: I get blood clots all the time, so I'm not worried about those) x