Help?

Ruba
Hello girls
I've had 2 miscarriages befor .. November 2015, February 2016, and now I'm pregnant again❤️
I'm now 6 weeks and 2 days, But I'm bleeding very dark brown blood !! My doctor told me it might be old blood and that I don't have to worry about!!! 
She also told me that if it gets worst and turns red , start cramping, then it's a threatened miscarriage 
She didn't do any tests though
Is that possible?? Anyone experienced this before??