Tightness and, sometimes, cording (which feels like weirdo guitar strings in your axilla and arm) is pretty common.
It's unlikely, after three weeks, that massage would do any harm. If you had nodes out--even just one or two--it takes a while for your body to figure out alternate pathways for lymph fluid, which is where massage can really help. Thing is, lymph massage is a specific technique quite different from what most physios do. Ask if you can have an appointment with the Lymphoedema nurse ( there is one in most larger hospitals) and get them to show you some moves. That's not suggesting that your symptoms arecin any way connected to lymphoedema, it's just a way to get a boob and armpit specialist onto the job.
It's all a bit of a nuisance, just when you think it should be over and one with. Marg.