One night I passed a grayish and flesh colored clump, Could I have miscarried?

I didnt think I was pregnant, and I got my period VERY lightly last month, lighter than usual. 

I was sexually active and was not completely consistent at taking my birth control pills, I think I may have ovulated before my period because mid month I had cramping and light spotting.

A week and a half after my light period, I started having heavy cramping that was primarily in my back and stronger than usual. One night I passed a grayish and flesh colored clump about the size of a quarter, with light blood streaking through it. I had cramping and light bleeding all the way until my next period time, and that period was really heavy. Could I be having these things because of my inconsistent birth control use? 

Or did something else happen?