Thanks for the query.
The possible causes for your bleeding are :
-Impending menstrual flow.
-In case of pregnancy
, there is possibility of implantation
bleeding or miscarriage
The possible other causes of bleeding in early pregnancy are : http://srsree.blogspot.in/2013/06/causes-of-bleeding-per-vaginum-other.html
imbalance leading to intermenstrual spotting.
Dark color of the blood usually indicates collected blood.
Once go for pregnancy test.
If the test comes negative, the possibility of pregnancy is less.
And you may get periods soon.
In the next cycle, you can track the ovulation and can plan intercourse around that period.
For more details : http://srsree.blogspot.com/2013/07/infertility-1_8.html
This will increase the possibility of pregnancy.