12 weeks, strong heart beat, spotting for 4 days

Kristin
I am 12 weeks pregnant, I started spotting on Monday, brown thick discharge, changed watery and now thick again. I was at the doctors yesterday and they diagnosed me with bacterial vaginitis and prescribed medications. I started spotting more after the pelvic exam and they said " the cervix was probably irritated" 
The heart beaT was strong at 150-160s, but I've read so much about brown being " old, good blood" and then read that others experienced this with a miscarriage. 
I am also under a lot of stress, and trying to start calm.
Anyone's advice or story of what they went through would be great!!