I am 6 weeks 3 days pregnant now?

I am 6 weeks 3 days pregnant now,went for ultrasound scan,gestation sac is 14.8mm and gestation age is 5 weeks 6 days.and yolk sac is there.heartbeat is yet to seen.they have seen one more sac(no yolk) size 7mm superior to the first sac.they have not confirmed that it is a twin pregnancy or a bleed.Radiologist told it may be a bleed.What is that bleed.?why they could see it ?