Pregnant. Started Bleeding. Ultrasound Shows Normal Sac And Heartbeat. Am I At Risk Of Losing Baby?

I am 6 weeks pregnant and bleeding brown, pink and even red blood for 2 weeks now. I had a scan and the sac was visible, then a week later another scan and there was a heart beat visible, the nurse said it looks good and has developed. She didn t explain though why I keep bleeding, all she said was bleeding is a threatened miscarriage . I wish it would stop, because its making me wonder wheather im at risk of losing my baby and its doing my head in. I didn t know you could bleed this much with bright red blood and still be pregnant, I m due for another scan next week, just wondered if this is normal and what does it mean.