Hi,
Welcome to the ehealthforum and I am glad to help you out. Amenorrhea during and after using Implanon IUD is a side effect of this contraceptive. But it is necessary to rule out any pregnancy as well. For confirming the status of pregnancy you should do the urine for pregnancy test after 1 week of missing your periods. Otherwise you can get serum HCG test or an ultrasound uterus done from your gynecologist which are more specific tests than urine tests.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.