I think my first bleed was at about 8 weeks, this was like you describe, a kind of brown dark blood, the sort they say is old and not to worry about. At 12 weeks I woke up in a flood of blood, I thought that was the end and headed straight to the hospital. The scan showed no reason for the blood and I was told to rest. Which I did but the brown blood continued to show everyday. It then stopped for a few days which was such a relief but then at about 15 or 16 weeks once again I woke up covered in bright red blood, we went to A&E and I was admitted. We had a day on a ward most of which was waiting for a scan, it was hard because the ward I was on is next door to the labour ward and there were babies everywhere. But once again the scan showed a healthy heartbeat and eventually after blood tests and an internal examination I was allowed to go home. The bleeding was lighter but when I was still bleeding several days later and I had a large clot come away I went back to the ward. Again to our joy the baby was ok, a bit sleepy but ok! After several hours in the hospital I decided I wanted to go home and rest there, it was easier to sleep in my own bed!
Anyway I'm getting to my point!!
After a couple of days of very light brown blood it stopped, I had spent the whole week in bed doing absolutely nothing. My partner made me packed lunches before he went to work and I only showered with him around because I'd been feeling faint. The good news is I havent seen a drop since!
I think that for some people its just the way it is, the Dr cant say why it happened, apparently its something that happens for alsorts of reasons that arent harmful to the baby. I hope that for your sake it goes away because I know how horrible it is, perhaps taking some time out and getting some serious rest will help you too? Anything is worth a try