What Are The Side Effects Of Using IUD?

My iud came out about a year ago while I was pulling my tampon out, I was very shocked cause I was told that is a one out of a 1000 chance it can happen; I never went to the doctor; I just went on with my life. I have not been able to get pregnant in a whole year; I started my period yesterday and I was just spotting, when I woke up this morning I was bleeding very heavily and I have been dropping blood clots for about 3 to 4 hours now, I am having really bad cramps too; can you tell me anything about what could be wrong with me?