I had unexplained pain like you. I had pain mostly when sitting for long periods in my back. Sometimes it would be in my thighs, pelvic floor or even my testicles. It would seem to move around.
All three of my interviewed surgeons stated with confidence that my pain had no association with my prostate cancer. But may have to do with an enlarged prostate. After my surgery the prostate was bigger than anyone had thought. I am a small framed man and it was thought that the prostate could be pushing against a nerve(s) etc. in certain positions.
I had a bone scan and a wet cat scan and they did not reveal any thing.
I am 20 days post op and I will wait a few more days to say anthing with conviction butttt, the pain I had everyday before is absent. They said it is a very remote possability that the surgery will do anything to relieve this type of pain.
Your pain could be from anything and you can see it does not have to do with cancer itself directly.