Bleeding

Nis
According to my sono, I am 6 weeks and 2 day old. I started to bleed 3 days a go, and at first it was light but now it's a little bit more pink and a little bit more heavier. It however is just spotting, and is not getting on my underwear. I did go to the doctor and when they saw the sono, they did see a baby but no heart beat. Do you guys know if it's too soon for a heartbeat? 
Thank you,
Nissan