What Causes Pain In The Arm After Inserting An Implanon?

I had implanon inserted three weeks ago and am experiencing some strange arm pain. Initially, I thought the pain was soreness from the insertion, but it's no longer confined to the implant area. The pain runs along the underside of my arm all the way to my armpit. It feels like a pulled muscle or tendon. There is a constant aching sensation and a tightness that has been bothering me a lot. In addition to that, about two days ago I noticed that some small bumps have formed in a straight line directly over the implanon implant. They are not visible, but very obvious when touched. They are slightly smaller than a pencil's eraser and extremely hard. If you could please explain these two worries, I would greatlt appreciate it!