I may not be of much help, @lowth21, but I'm prompted to mention a couple of possibly pertinent experiences. For background, my cancer was in the bladder, not the prostate, but was discovered after a TURP procedure to alleviate benign prostatic hyperplasia. Another difference for me is that PSA tests are of no value in cases of bladder cancer. A total of 12 small, low-level malignant, epithelial polyps were later removed from my bladder by a TURB procedure.

First a question: What can you tell us about the "doctor (who) believes your sciatic nerve was damaged?" About a year after my bladder surgery, I developed pain in my pelvis, buttocks, and thighs. My primary care physician (PCP) sent me to spinal pain specialists, who quickly pointed to my sciatic nerve as a prime suspect, ordered an MRI, suggested I get ready for spinal surgery, and told me to start taking steroid shots to alleviate the pain. All of these fit into the daily routine advice from the spinal pain unit. But first, I needed six weeks of physical therapy, they said.

During that time, I did some research and talked to my PCP a couple of times about possible diagnoses. We settled on trying an anti-inflammatory therapy that only becomes a diagnosis if it works! Looking for a root cause, we assumed it might be inflammation of one or the sacro-iliac joint where the spine connects to the pelvis -- perhaps an after-effect of either the TURP or the TURB surgical procedures. She arranged for injecting one joint with an anti-inflammatory medication, and within a few days, the pain was gone. A second injection was never needed.

This result may be coincidental rather than causative, but I thought you'd like to have it as one of the ideas to discuss with your "doctor." Keep us posted so we can learn from your experience and, hopefully, find other questions you can put to your medical team.
Martin