Hi - Take some deep breaths and try not to panic, OK? What you describe doesn't sound at all like breast cancer symptoms. You've had both a mammogram and ultrasound that were normal; that should give you some comfort that this isn't cancer you're dealing with, but something else.
When you have multiple lumps in your breast, that's often a sign of fibrocystic change, which is fairly common in younger women. It can be quite painful, as oftentimes cysts develop, and as they enlarge they can press on nerves. And this does sound like a nerve issue, with pain traveling down your arm. It could very well be that your implant is positioned so it's pressing on a nerve, too. Unfortunately, there's not much you can do at this point beyond work with meds to try to alleviate the pain. Has your doctor prescribed anything yet? If not, make sure to let him/her know how much discomfort you're experiencing, and that you need some relief.
Again, please try not to stress; pain in the armpit, and traveling down the arm, isn't a typical breast cancer symptom. In fact, breast cancer is usually painless. And remember, you've had screening that's come back normal. Please read our post on fear as you wait for your appointments; I think it might help you. Take care - PJH
P.S. Here are some other links that might be helpful for you:
Can Olive Oil Help Prevent Breast Cancer?
10 Breast Cancer Myths Debunked