James, I had the same PSA nadir six years or so ago following prostate removal and my PSA alas continued to rise, necessitating further treatment. With no prostate to restrict the urine flow, I guess attention has to switch to the urethra, where I have a met still (subject to my next scan showing otherwise. I hope!), the ureters or, worst case, the kidneys. In all three circumstances, the PCa is treatable. I would be pressing for an earlier scan if the flow problem is not simply anxiety based but reflects the three possibilities I mentioned.
Good Luck
AC