It should subside over time, in most cases, but with surgery it may be longer. Lymphatic drainage massage has to be done in a certain direction, path, pressure, and each area is different, so would suggest seeing a professional, get the doctors clearance, and massage is not done with a fever, infection. Did you have a post treatment scan yet? I wonder if doing so can do harm with any reminiscent tumor? After several visits, instruction, you may be able to do some on your own. Light exercise, such as walking, swimming, will help with the lymph flow, swinging arms over head, trampoline, sweating, compression bandage, also help, but see your doctor before attempting anything. Good luck.