What Causes Tender Breasts While On Implanon?

hi i am a 24 year old female, i gave birth to a stillborn in july 2006 at 37+3 weeks, before i got sent home i was given a tablet to stop me from producing milk, i fell pregnant again around 4 weeks later and i lost the baby at 8 weeks, i then decided to get implanon inserted as i decided my body needed a break from the trauma, shortly after i got implanon i noticed my breasts were tender, my left breast was alot more tender than my right (i have the implanon in my left arm) i have had this tenderness for 3 and a half years now, i havent spoke to my own doctor as i am embarresed, i do regular breast examinations and i haven't noticed anything abnormal! i also gently squeeze my nipples and no fluid of any type comes away, i have no family history of breast cancer, i am just wantig to know if this could be a sign of breast cancer! thank you in advance.