Infection in blood and High creatinine.

My mother Aged 58 years , diabetic patient was suffering from fever for almost 1 month. Her blood test shown infection which has gone with medicine. After few days again she started to develop fever and shivering. Further she develop pain in one side of her back along with nausea. Her tests suggested increase in creatinine and Urea levels. Her CT scan doesn't reflected anything In kidney but blood test shown infection. Now after 2 weeks of antibiotics medication her condition has not improved much and today again in her CT scan nothing is detected in her kidneys. Than doctor advised for PET scan that is also normal but her urine report is reflecting urine infection. Kindly suggest for future course of action as her Urea and creatinine parameters are not improving much and doctor is unable to trace the source causing infection in the blood.