Great to hear you have an appointment booked. They book up really quickly, don't they?
Sorry, I don't know about it in the breast area. Maybe keep up the massage that they showed you at the hospital. I had massage down my arm, across my chest and under my arm. The lymphatic system is all connected so it couldn't hurt. There are lymphoedema organisations that could give you more info.
Exercise, like Pilates, is helpful with lymphoedema too. I'm sure some of the other ladies will have some more useful ideas. I hope everything settles down. My hand was so swollen after chemo and the area under my arm was so swollen after radiotherapy and they settled down in the months afterwards. I know it's really stressful to have this. x