What Are The Symptoms Of Potential Miscarriage?

I have had abnormal cramping, and bleeding. I did just start the birth control pill. And I figured that's what it was from. But I did have unprotected sex before starting the pill and a few days after starting. But both times I took plan b. I never took a pregnancy test. I got my period at the beginning of September. I was told that I shouldn't get it again until I finished the first pack of pills. I started to bleed the beginning of this week. It was not like my normal period. Heavier and less consistent. I never usually get cramps. When I do they are mild and only last a day. But this week they lasted 3 days and were so bad I couldn't sleep. I still figured I was a special case and the pills were causing it. It wasn't until just now I thought of the possibility of a miscarriage. What do you think?