My father is 49 year old. He has type 2 diabetes for over 9 years . He has fever and body pain for the last 1 month, the temperature keeps fluctuating the entire day (99.5 °F-100.5). He has no other symptom. We had got done a few tests like blood haemogram test, urine basic and culture test, typhoid widal test, stool test, ultrasound and X-ray for the whole upper abdomen...all the reports were normal. Would could be the possible reason behind the fever ?