Is Heavy Clotting A Sign Of Miscarriage?

Hi I had the fallope ring procedure done in november 2011 for a tubal ligation. This month ive been experiencing pregnancy symptoms ie heartburn sore breast moddy tired etc. And was lare for my menstrual until last night(4 days late) it started light but bright red. At noon today I changed my tampon and by 2 I was rushing to the bathroom cause I could feel the blood coming out of me. I removed the tampon and was covered in clots. I kept wiping and getting more and more clots and slimy bright red blood. I have had terrible cramps and really bad headache. Im afraid I may be miscarrying.....is this possible? Oh and im also not bleeding as much anymore but it is still bright red but have only changed my pad once since 2 this afternoon and it is now 11