What Causes Persistent Pain In Sciatica?

I am 25 yrs old and 7 wks out from PC-Rplnd. I am having sciatic pain that has lasted for over two weeks now. I had a 100% yolk sac tumor removed during the Rplnd. It was grown into the vena cava which had to be resected and grafted. I am concerned that the sciatica is from compression from new cancer mets. My AFP had gone done from around 80.5 to 40.4 two days after surgery. My local oncologist has ordered an MRI and bone scan, then CT. What are the chances something new has developed since my surgery?