What Could Have Caused Large Blood Clots Like Tissue And Lower Stomach Pain?

I'm 27 yrs old, and I've been trying for a baby for like an year, so i don't use any contraceptives. last month, my period was delayed for a week and all of a sudden, i got a HUGE clot. it was about 6 inches long and 3 inches wide at one end n the other end was narrow. then i went to see my doc and found out that i had an early miscarriage, and was under medication since then till 2 days back.And i was told that i dont need a dnc cos i was clean. But i still have on and off minor bleeding and sometimes alot. And yesterday evening i got a very severe pain on the right sight of my lower abdomen. i had to take a pain killer and it slowly went off. my blood tests show that i was negative to the pregnancy test, but doctor tells i was pregnant. could this be a miscarriage or a sign to something else? i am a hyperthyroid patient too and ran out of medicine on the same day of this heavy bleeding.