It sounds totally normal to me... I had reddish brown blood at 5 weeks for 4 days with my first pregnancy (enough blood for a period), and my doctor told me it was just old blood coming out. BTW, I also had bright red blood (though just a little on tp and in the toilet) at 7 weeks, accompanied by cramping. Both times I thought for sure I was miscarrying, and all was fine. No other scares after 7 weeks. Good luck!
I experienced some minor bleeding at 6.5 weeks. First it was brown, then it stopped for about 24 hours, then it came back again, this time reddish brown. It continued for about another 24 hours - I even passed a few small clots. The first u/s showed "questionable heterogeneity" around the placenta but a strong hb - this was during the 24 when I wasn't bleeding. When I began to bleed again, we thought it was over, but a second u/s showed an even stronger hb and no sign of the weird stuff around the placenta. My doc thinks maybe the bleed was my body getting rid of it.
The point is you can have bleeding that is benign, but you should always see your doctor to be sure. Brown blood is better than red blood because it most likely means your body is just getting rid of old blood. I learned that 1 in 4 women will bleed during the first trimester and 50% of those women will go on to have a healthy pregnancy.
But brown blood can also be a sign of a missed m/c, so definitely get it checked out.
It is probably too early for the u/s to pick up a hb, but you could have your HCG numbers tested 48 hours apart. If the numbers double, the pregnancy is most likely on track (even if they only double every 72 hrs, you're probably ok). And then you should be able to have an u/s fairly soon - maybe even at the end of this week.
I wish you the best - I have been in your shoes.
I have not heard of the drug, but I have heard that brown blood is much better than red as it means it is old blood and not fresh blood. Did you get an US when you went to the doc ? or somehow check for a heartbeat - may be too early to detect one but I would just ensure my doc keeps an eye on me as the weeks go by. I would also keep tabs on what is happening down there and if there is red blood to see medical help ASAP! Good luck - no need to worry until there is need to worry!