I understand implanon is a progesterone based implant? All progesterone only contraceptives have bleeding as a possible side effect.

The Family Planning Australia website says this:
WHAT SIDE EFFECTS ARE LIKELY?

The most common side effect is irregular bleeding which can vary from no bleeding at all to troublesome frequent bleeding. Other side effects are rare but users sensitive to the hormone in the rod may experience side effects like headaches, weight gain and breast symptoms.