What Causes Blood Clots In Vaginal Discharge During Pregnancy?

Hi, I think I miscarried on January 2 because I passed big blood clots about the size on my thumb. I would have been 4 weeks after conception when my miscarriage occured.
Now, my question is the following.
1) Is it normal that after passing the blood clots I bled but very lighly. Meaning, I bleed a little bit everyday, but in a week I don't think I would have filled a pad.
2) After a week, is it normal to still test positive with a pretty dark line to pregnancy tests.

I have to say I'm very confused and I have yet to hear from my doctor.

thanks,
Evelyne