What Causes Brown Vaginal Discharge While On Implanon?

I had a implanon inserted one year and 2 months ago after insertion I had bleeding for aprox 3 weeks since this I have not had a single period since now all of a sudden Out of the blue i had a period very dark brown lasted a week then stoped then a week later today it starts again very dark brown I have only had one week with out bleeding how long will this go on for am i pregnant I am seriously considering geting it removed