It can certainly take some time for your cycle to return to normal after using implanon. The initial bleeding was likely to be an oestrogen withdrawal bleed, and your OPK may be a bit confused by synthetic hormones still being present in your bloodstream (and saliva). Don't be concerned, things will settle down. Charting will just be a little more confusing for now, so just do your best and record as much info as you can.

Use your OPK anytime you notice fertile cervical mucous (watery or raw egg white consistency) and record day one as the first day that you have menstrual flow (as opposed to spotting).

All the best
xxx