Tender And Achy Breasts, Cramping In Lower Abdominal Area, Dark Brown Discharge. Is It Miscarriage ?

I have had very tender and achy breasts for 2 weeks now. I started cramping in my lower abdominal area 2 days ago and I put on a pad, when I saw it later that night it was loaded with very dark brown almost black fluid. I wiped and it looked like poop. I had very severe cramping yesterday and when I went to the bathroom I passed a large flat piece of skin looking tissue. It had some black spots on it but was overall pink in color and was about the size of a playing card but in a triangular shape. I have never passed anything like that out of my body. Midol or ibuprofen did nothing to take the pain away. Today my stomach still hurts and I am bleeding lightly. Did I suffer a miscarriage or what could it be? I have had unprotected sex for about a year, and I missed my period this past month.