Both PSAs of 3.5 and 4.5 are high and you should check for the reason. The increase (1.0) in four year is small. I wonder why you did not address the matter four years ago and had a biopsy.
Many things can affect a high PSA, sometimes doubling its numbers. Any activity that could place strength in the prostate a day before drawing blood would cause a spike in the PSA. Riding motorcycle or cycling would do. Even sex the night before or passing hard stool could cause a substantial increase.
An infection could also be present, causing an increase in the size of prostate due to inflammation, and that too is related to high PSA.
I would recommend you to have the PSA tested before the biopsy if the last test (4.5) were done three months ago.
A biopsy is a simple out-patient method of testing that will rule out the presence of cancer and give you peace of mind. Do not let time pass without checking the problem.
I hope your case is not cancer but many guys in this board including myself have been caught at the young age of forties. I was diagnosed with prostate cancer on my 50 years old, eleven years ago, but now I believe that cancer existed since my 46. Remember that prostate cancer caught earlier have many chances of cure.
Hope you get that answer for the good side.