Fever on and off from one month.

First fever on and off  in blln 99 to 99.8 Widal negative after 5 days ,till then same continued after 11days again done Widal positive o&h 1:160 treatment taken antibiotics like ornio,azithromycin 500mg 5tabs,moxinow 4tabs  during this fever pattern is same  after 5 days again test for  Widal done o&H is 1:40 (negative),esr 26 but still fever is from  99 to 99.6 in morning it is normal when went outside it will goes to 99.2 and at afternoon it is 99.4 to 99.6 and at evening at 8pm it may subside to normal during this I has headache, bodypains,stool analysis done no cyst no ova ,mucus present 2to 3 puscells,doctor given rifaxin 400 thrice a day,earlier also rifagut 200 taken during 7th day now today is 32 day,what is the reason for this , Thyroid normal ,bp normal,chest x-ray clear,what is the reason for the on and fever 99 to 99.6 ,what blood tests are needed to evaluate this issue,hoping for detailed explanation