after thinking back I also had this same weird bleeding last month as well I was about 4 days late last month and it came on after me and the bf dtd. it started out that same brown discharge and then light spotting for two days then back to the discharge for a day. could I be 10 weeks along and just not getting a positive hpt. I tried calling to schedule an apt today at my doctors but there office was closed for some reason... ugh...
Seek medical attention you may be experiencing an ectopic pregnancy
I would wait another week and test again. Dark blood is older blood so it could have been implantation bleeding.
From my experience, its better to have it checked by the doctor, hope its a good one:)