What Causes Prolonged Bleeding While On Implanon In Arm?

hello , iv been on the inplant (in the arm) for seven months , i started bleedin straight away and it wouldent stop so i went to family planning and they gave me the contrapseptive pill, it stopped after a week. i had a good few month with no bleeding at all and now its come back iv been bleeding non stop for 2 weeks now iv been taking the pills that were left over but its not working this time . what should i do ?