is there anything wrong?

Hi guys! I was on birth control and I had to stop it about three months ago because I changed doctors and my prescription with my last doctor was up. So I finally got my prescription about two months ago and I waited to get my period. It never came in October. I took a pregnancy test before starting my birth control again and it came out negative. Right now I'm having terrible period cramps and I've been having them for about a week now. My cramps usually on last about the first two days and that's it, but these started before and is still going. My period is just brown substance coming out of me. This morning I went to the bathroom and I had a really big blood clot around all the brown blood. What do you think it is? Is this normal or should I think of miscarriage or?