It could be entirely possible that it is from the implanon. Some women will get bleeding at the start and then nothing for the duration and some will get bleeding on and off similar to AF the whole time.

I got this from the implanon-usa website;

<H3>How will my bleeding change?


Expect your menstrual periods to be irregular and unpredictable throughout the time you are using IMPLANON?. You may have more bleeding, less bleeding, or no bleeding. The time between periods may vary, and, in between periods, you may have spotting.

You should discuss any questions you may have about irregular bleeding with your Healthcare Provider. Be sure to let him or her know if you think you may be pregnant or if your bleeding is heavy and prolonged.
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Also moving this to the Contraceptives forum....