Could it be a misscariage?

Signs of a misscariage...? I've been bleeding super heavy for just over a day now I woke up in a pool of blood and when I went to the washroom I had a blood clot just bigger than a quatre. I have bad back pain and had worst cramps then I've ever had on my period I was very light headed the day before I started bleeding and am going through a super tampon atleast every 1.5 hours

. I had to take a plan b about three weeks ago but I was on my fertile window so it was pointless could I of had a misscariage? And what do I do