Pain from lymph node enlargement

I have stage IV rectal carcinoma. I developed back pain 6 wks following peritonectomy and intraperitoneal chemotherapy for carcinomatosis. Unfortunately a CT scan and biopsy revealed large lymph nodes with metastasis next to my aorta not present 8 wk ago. NOT good. The problem right now is pain. Percocet controlled it for 2wks fairly well but then it got more intense. Yesterday started oxycontin with oxyconone as needed. This is not helping much and I need to talk with my oncologist about changing dosage etc. I am suprised that mild to moderate lymph node enlargememt could be so painful. The largest node is 1 inch diameter. Anyone else have this experience?