Fever after Hysterectomy. By it's own?.

My mother had an Hysterectomy operation 9 days back. After that , she is having persistent fever which is ranging from 99-101 . After the dose of paracetamol, it's coming down but after the effect of medicine is over, it's coming back again. Postoperative tests has been done like urine test, infection test near operative area. No infection is found. Asking my mom about her health, she is saying that she is feeling okay and having no issues while breathing, walking aur having any pain near operative area. The only problem is fever which is not going. It's been 10 days now. What can be the possible reason for this. Will it go by it's own ? . please provide me information regarding this as I am worried. Doctors are monitoring her and  are saying that they will discharge her after some days with antibiotics please tell me any solution of this,. What test should I do ? Or It will be okay after some days.?