Does Implant Causes Brown Discharge?

hello, i am 19 and have had the contraceptive implant since beginning of september 2010. it stopped my periods up until about a week ago. when i experienced a period at my due date. i went to doctors. they told me it was normal. i stopped bleeding after a couple of days but then 2 days later i started bleeding again. this time really thick brown/black blood. is my implant still working?. and why has it just affected me now?