Welcome to BB!

If your period is still missing in action 18 days after your positive OPK (ovulation prediction kit / test) then it's time to do a HPT (home pregnancy test) to see if his spermies caught your egg!

Best of luck!

By the way, I read an article that suggested all effects of implanon *should* be gone by 3 months, and conception in women after implanon removal is no different to all other women by that time. I had my implanon removed, then had a anovulatory cycle, and then conceived 12 cycles later. HTH!