Ask to see a LANA certified physical therapist. That is a PT who has been certified by the Lymphedema Association of North America. Regular PT isn't enough. You need CDT (complete decongestive therapy) which is a form of gentle massage to get the fluids that have blocked up near the missing lymph nodes flowing to other branches of lymph nodes. If it is caught early enough, it may be reversable or at least better controlled. I had 26 lymph nodes removed (only 3 were cancerous). My oncologist blew me off and I didn't get treated until it was stage 2/3. Do not let your oncologist blow you off. If she/he does, insist on a LANA certified physical therapist. If you have to change oncologists to get the proper referral do so. The first oncologist sent me to a regular PT. I had five months of useless therapy. When I learned that I needed a LANA certified therapist, I changed oncologists. I now struggle daily with keeping the swelling down. I have to use compression 24/7 and a pneumatic pump. I still struggle with with episodes of lymphangitis, which send me to hospital for IV antibiotics. Do not let anyone take your BP or give you any kind of injection, such as a blood draw, IV or vaccination in that arm. Last time I had lymphangitis my arm swelled up to 27% larger than my other arm. My hand looks like a balloon. Getting it down again is a nightmare.
I just had an evaluation for surgery at one of the Lymphedema Centers of Excellence.

If you are overweight, try hard to get it under control. Obesity plays a role in making lymphedema worse. Actress Kathy Bates has lymphedema. She is the spokesperson for the organization LE&RN. She recently lost 100 lbs and she said it helped her lymphedema greatly.
Check out LE&RN (Lymphedema Education and Research Network. They provide a lot of information.
Good luck to you!