Dear sir i understand your concern. By above information i am able to make out that some surgery was done.infection is most common cause of fever especially post surgery. kindly let me know what kind of test was done before. is his diabetes under control or no if dad is staying in home i suggest you to record his temperature once hourly to understand the pattern of fever.With a thermometer is not Difficult job. There are many levels of test to be done ranging from total counts to Blood cultures.even after doing every thing if we are not able to find solution then its called as PUO pyrexia of unknown origin. Very rarely underlying cancer will also present with fever of continues nature. I suppose I have given the desired response if you have any other query please write back. Otherwise please accept & rate my answer. I will appreciate your review about my answer. Best Regards. Dr Vamsi Krishna Consultant Diabetologist