Hello, Most of time fever suggestive of infection in body somewhere, but not always. Sometimes due to inflammatory response of body show temperature. In your case, the Kidney infection could be the main cause of fever. But you also mentioned the TLC count was very low initially. This low count itself causes fever called neurogenic fever. Mostly seen in chemotherapy induced or in Maliganancy. In your case, it may be due to antibiotics. As you asked about duration of fever regarding kidney disease. Actually it depends on the type of pathology in kidney. The infection in kidney for prolonged time itself is a very high risk condition. Because this will lead to damage if kidney irreversibly and patient may developed chronic kidney disease and dialysis. Or may sometimes this infection spread all over body called sepsis and may be life threatening. So proper work up is necessary to find out the extant of kidney infection and to find out exert pathology with organisms. So that proper treatment should be initiated according to severity and specificity of antibiotics depends on organism. So go for CT Abdomen for Exetent of damage and Urine culture for sepecific organism and specific drug to cure this infection. In this case better start Clindamycin and antigungal drugs also to cover the spectrum. Overall, this case taken seriously and treat according to that as early as possible to avoid critical conditions. Thank you