ADJ, take a look at my profile where John's PA results are listed. Following RP 10 years ago and then salvage RT 8 years ago, his PSA crept up and has bobbed along at between 0.1 and 0.11 for the last 3 years. He continues to have 3 monthly tests and regular reviews with the urologist and / or oncologist but we have no intention of doing anything until there is evidence of a problem. The onco has said he will arrange scans if it rises significantly and targeted RT if there is a visible recurrence away from the prostate bed but since it has stabilised, it may just be that he produces a high level of 'healthy' PSA. We are not concerned and I don't think you should be yet, either.
The thing about waiting until it gets to 5 does make sense, believe it or not, although some oncos say that they would wait until 10 or even 20. There is a difference between the level at which it is accepted that there is a recurrence (0.2 or 3 successive rises above 0.1) and the optimum point at which to reintroduce treatment, particularly as the treatment will usually be long term HT and is not curative. HT has a limited lifetime of usefulness so the earlier you start taking it, the earlier it will stop working. Waiting until the PSA gets to 5 or whatever means that you have delayed the time when you run out of treatment options. I imagine that you could press for scans once it gets to 2.0 rather than wait until it gets to 5.