Miscarriage or period

In March I had a rather heavy period. One of the days was the worst pain I’d ever experienced; severe bleeding, pain that I assumed was cramps and hours of being sick. I couldn’t get myself out of bed to the toilet I was in that much discomfort. It went on for hours and then during the evening this came out. I’m used to clots but none this big with that much tissue. I had had unprotected sex but had taken the morning after pill and thought nothing of it. I had the thought in the back of my mind that it might have been a miscarriage but I never took a pregnancy test. Could anyone explain whether this is just a severe blood clot from a period or was what I experienced a miscarriage? This would have been about six weeks after unprotected sex.