I m on implanon and haven t had my period in a year. Out of nowhere, I got cramps and the next morning woke up with bleeding. Also, I ve been taking topamax which I know decreases the effect of the birth control, what are the chances I could get pregnant?
Tokamak should not decrease the effect of the implant, though it could decrease the effect of birth control pills.  Also, some people may have an irregular period on the Implant, even if you have gone for a long time without a period.  As long as it is not very long or very heavy you don't need to worry about the bleeding.  I hope this helps answer your question, please let me know if you have any more questions.