Lymphoedema under arm post surgery

Hi everyone. I am 18 days post tumour and axillary lymph node clearance  and have developed terrible fluid swelling under arm and side of breast. I had half a litre drained last week and will have it drained again on Thursday but has anyone any tips to reduce it? It’s so painful! I have been doing my post op exercises 3 times a day I have near back to normal movement but this terrible swelling!