Call your doctor. Passing blood clots is not normal, call your ob&gyn doctor or go to er thy will find out the cause, do not wait.
Possible miscarriage. 1 in 6 pregnancies results in spontaneous miscarriage, often with miminmal symptoms (early--less than 12 wks) and only just some bleeding/clots like you have. I would check with you doc asap to confirm. Maybe a speculum exam and/or an ultrasound, and possibly blood test checking for the hormone of pregnancy--hcg (human gonadotropic hormone) level etc... Best of luck to you.