What Causes Heavy Periods And Lower Back Pain While On Implanon?

i had the mirena and it was removed about two weeks ago because i was in major pain. i could not feel the strings so they had to go in ther and remove it and after that... (same day) i had the implanon put in and ever since its been 14 days now i have have heavy bleeding and really bad cramps in my abdomen and my lower back i dont know if its just side effects or a possible miscarriage?