Breakthrough Bleeding?

I missed 2 pills (i've not been having so its ok) and two days later i've started to bleed really lightly... except its dark brown and almost black in colour and every time i urinate little bits are in the toilet... gross i know sorry haha... ive continued to take my pills...anyway ive been bleeding for a week tomorrow and its not showing any signs of slowing down and its really annoying me... can any one think of ways to stop it or any idea of when it will stop? Thank you!