I am also on implanon, and i bled for an entire year straight, no cramps, no probelem other than becoming anemic, but a year straight with maybe a week total of time where it stopped for a day at a time. Nothing to worry about, i called implanon (the number is on the card they gave you when you had it implanted) and they said that is usual in some women and it normally corrects itself around teh one year period, which mine did. now i have periods that are much calmer, still sometiems off, but no where near as bad.
Irregular bleeing is common when you first have placed. However, if it is persistent or heavy, you should check with the provider who placed it.