I have read your question,
Without examination and medical history , it is difficult to say that the symptoms you are experiencing are due to Implanon
Implanon(nexaplanon) causes few side effects but the chances are quite less.
Some of the side effects are abdominal pain
, loss of libido,vaginal dryness
and Irregular bleeding and spotting .
The rash you are having may be due to vaginal dryness or sanitary napkins or inner wears .
So I suggest you to consult a gynecologist nearby for further medical advice
Wishing you a good health,