What Causes Heavy Clot Discharge During Mensuration?

Hi am rad,i was 8 days late,i had an Ultra scan and i realised i was pregnant but my UPT test also proved negative. I started bleeding 3 days after and it lasted for 5 days which is normal for my period,i discharged very heavy clots during the bleeding accompanied with very severe cramps. Am done but still have symptoms like waist pain,slight headaches,very frequent urination,diarhea,severe abdominal cramps and gas in my stomach.i cant lie on my tummy anymore because of the pains i have.plz help me am worried.