Bleeding but still pregnant

I have been bleeding on and off for almost a week. When it first started I went to the hospital (tuesday) and they said my levels were still doubling but couldn’t see anything on the ultrasound as it was too early. 4 days later I went back due to my bleeding being heavier with a small clot. My levels still doubled and they saw the baby and heartbeat on the ultrasound. I’m exactly 6 weeks. I have my first prenatal appointment in 3 days but I’m still anxious and curious to see if anyone else went through this and had a positive outcome. Eases my mind knowing the baby is growing although I’m bleeding and passing clots but not sure what would cause that.