What Causes Prolonged Bleeding While On Norplant?

hi,im 34 yrs,56kg,152.3cm,i am on norplant for 8 months now and have never had any problem but for the last 1 month i hav been bleeding n was advised to use cosclot 1 tablet three times daily to reduce bleeding,bleeding is still there,changing 2 pads 24 hrs.pls advise me