Help! Horrible period or miscarriage?

All day at work , my back was killing me and I had horrible cramps throughout the day so I figured I was getting my period because my period is never really on schedule . There was blood but not drastic amounts so I just wore a pad and kept changing it as normal. As the day progressed though , cramps got worse so I took medicine. When I was getting ready for bed , it felt like I peed sort of, I dont know how to explain it , but blood was pouring down my leg and i ran to the bathroom to wipe and it was clumpy and gross. I'm really freaked out because this has never happened to me. Sorry if its TMI , but like I said I need help ! Thanks for any answers