Temperature changes in a day.

I'm male 24 yrs ,earlier body overheat normal temperature after 3 days temperature changes in between 98 to 99.8 widal negative again after 5 days widal o&h 1:160 taken antiboitics like gudcef,ornio,azithral,moxinow for 14 days ,then Widal negative antioiotics stopped for 1 mnth,but still temperature pattern is same,esr 25,chest x ray normal,mantoux normal,thyroid normal,us abdomen normal,no abnormal cells,CRP  6,smear for mp negative,taken doxt-xl antiboitic for 5 days blood test done esr 25,widal igg&igm negative,blood culture negative,twbc 5600,trbc, 6.3 Millon's, platelet 1.65laks,pcv 60,on 60 th day went to doctor prescribe to do some tests CRP 6,RF assay negative,scrub typus negative,ESR 10,,Here ESR reduced from 30 to 10 ,but my temperature during 2 mnths is same morning after 8am increases to 99 afternoon goes to 99.6 ,sometimes 99.8 ,evening after 9 or 10pm it is normal,doctors pls tell what is the reason for this variations in temperature.