Perhaps your PSA is residual from pre sugery and still going down?
My first postop PSA test was taken at 90 days/13 weeks and reported .19
Repeated test 30 days later at .18
My understanding is PSA greater than .1 postop is called "persistent" and I was then treated with Salvage Radiation and ADT.
Prostate Cancer Foundation pcf.org has downloadable free Patient Guides.
Good wishes