You don't say what your other halfs staging and Gleason score was?
I would recommend plotting the uPSA scores on a graph, if it's natural "regeneration" of any remaining healthy prostate tissue left behind (this can happen at the bladder neck apparently) the graph will tend to flatten over time with the odd blip due to the vagaries of uPSA testing.
If it's a prostate cancer coming back the graph will not flatten and will tend to rise exponentially.
Either way provided you didn't have any adverse pathology in the removed prostate you will have time to wait for more 3 monthly tests to confirm. Fingers crossed the next test is the same or less.