Hi I Have Had The Contraception Bar In My Arm

Hi I have had the contraception bar in my arm for I'd say about 8 months now,I have never had any problems with it what so ever but around last week k was feeling it and it feels like there's a lump just above half way of it and I am a bit worried about it,its not sore but I don't no what it is and the bottom of the bar you use to be able to feel it but now you can't feel it as much and I'm afraid incase it has snapped if you could tell me what it is it would be great,thanks :)