I agree with sentiments here....don't take your doctors word for it-especially if it is just your general physician.
I have had two Uros and my primary care physician take a keen interest in my prostate (one of the Uros removed in on June 1st because of cancer). All three knew I cycled a lot, but never said anything about cycling causing Prostatitis.
The only thing they would agree on concerning cycling and the prostate is that a PSA reading can be elevated because of bike riding (along with other activities). So it was recommended not to ride my bike (or have sex) for 3-4 days before a PSA test.
Dan