UTI's can be very difficult to overcome and sometimes need more than one antibiotic. So could understand if GP wants to monitor for a time. If symptoms persist or PSA doesn't fall, I think it likely your GP will refer you to urology. They will wish to rule out UTI by doing a culture test rather than a dip test if this is all that your GP had done. An MRI may then follow and dependant on this and other indications possibly a Biopsy. But things have to be taken one step at a time and the next being that you are definitely free of UTI.