Unexplained bleeding?

Has anyone experienced unexplained bleeding in their pregnancy and had positive outcomes? I am currently 8+6, and had brown spotting before my 7 week confirmation ultrasound. The spotting comes and goes. But then today I woke up to a gush of red brown blood and clots. Had an emergency ultrasound, and no SCH or any explanation from the doctor as to why the bleeding is occuring. Baby was still in there with a heartbeat, although it was 146 today and 156 last time. (The drop in HR also worries me.)

Any bleeding stories?