possible miscarriage

My AF was 2 weeks late I took a test and it was negative. The next day I started bleeding and cramping  really heavily. My cycles usually are light and hardly no cramping. When I pulled out one of my tampons there was a dark red kidney bean shape and sized clot. It was very firm and not squishy. It didn't come apart like normal clots have done. I almost never clot. I have been feeling super tired and nauseous. I took a test the next day and it still said negative.