What Causes Light Bleeding After A Year And On Implanon?

I have had the implanon implant for over a year now. My periods stopped all together for the year and i havnt had any problems with it but over the past few weeks i have had extremly light bleeding. It was heavy for a bout 2 days and the rest of the time its been so light that it can barely be considered a period. Why is this happening when ive had no problems for a year? I thought it was supposed to settle after a year not get awkward? x