Hi! My Brother Has Just Gone Through A Kidney Stone

Hi! My brother has just gone through a kidney stone removal surgery.the doctor has placed a stent in the urater as according to him there was a blockage in the urater due to which the small stone could not pass through itself even after a week long medication.the doctor said tat the stone had created an infection in the urater so they had to put the stent so tat the tube does not stick .but now even after antibiotics my brother is having fever since past two days.the fever is coming after every 6-8 hrs n it's a mild fever.all blood sugar reports are absolutely normal.can u plz tell me tat wat can be the reason for his fever even after the surgery now.