As you've altready found there are a lot of views & theories about PSA:
Lee Nelson in his book "Prostate Cancer Prevention and Cure" suggested that 70% of PSA's between 4 and 10 are traced to benign causes.
Although your PSA seems high for age, there is no "normal" reading. It's correct that the trend is of interest, especially sudden rises. Other things can also affect it in addition to infection:
DRE and Sexual activity can have an influence on PSA, so best not to have the test too soon after.
PROSTATE SIZE: Theory is that the larger the prostate the more PSA it produces. The Prostate size is needed to calculate PSA "Density" which is PSA divided by size of prostate. Johns Hopkins research into "insignificant cancers" discusses this aspect.
Results can vary a bit, but as it reduced to some extent in a short time, yes I'd also be monitoring the PSA for now, and thinking of the other aspects like the density, trend, free psa which have been suggested.