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It is difficult to comment on the effectiveness of your Implanon without examining you and going ahead with getting further evaluation. Consider visiting your doctor/gynecologist for further evaluation and assistance. If worried, use back-up protection for additional protection while having intercourse, and avoid having unprotected sexual contact if you are not ready for pregnancy. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately.
Take care.