What Causes Heavy Vaginal Bleeding Along With Clots During Pregnancy?

Hi i just need to know i had heavy bleeding and big cloths that came down all at once and then it minimized during the day and just had brown discharge afterwards .Was it a miscarriage or just implantation bleeding.I didnt go for an ultrasound, i went to the doctor a week after but my test was still positive i lost most of my pregnancy symptoms but my tummy gets bigger during the day and looks like im pregnant is it normal?.Must i go for an ultra sound to see if the baby is still alive but the dr didnt send me she told me that my heart rate and pulse aint normal yet that was a week after the mc