I do believe you are jumping to some illogical conclusions.
this all sounds like typical muscle issues.
I do know something about prostate issues due to my hubs.. what I do know is that ONLY advanced prostate cancer causes back pain. this is directly from the doctor who sees my hubs about his prostate issues. If your back pain was associated with prostate cancer, you would have had significant issues long before back pain.
SO do yourself a huge favor and unload the idea of your back pain being evidence of prostate cancer.