Hi, My Father 64 Years Old Under Went Prostate Surgery

Hi, My father 64 years old under went prostate surgery (TURP ) one year before. Soon after surgery he faced urinary track infection frequently. Now for the past one month he is having fever then and there. Doctors diagonise e- coil bacteria as a cause of infection and fever. They prescribe anti biotics but once he finish his course he gets fever again. Today he under went sonography and found prostate enlarge meant again and kidney stone of size 16 mm* 16mm. Pls advice what to do and tell the exact cause of his frequent fever.