What Causes Brown Spotting And Blood Clots During Pregnancy?

hi i had a misscarriage in december and im pregnant again just 6 weeks 3 days ago i started to lose a brown discharge then a day later it turned to blood with small clots i have been haveing what seem to be contractions i seen the doctor today and she said my cervix are closed and its a 50/50 chance .the last time i had a misscarriage it didnt take this long i lost big clots within 24 hours and didnt have these pains please give me some advice im loseing my mind