About the reson of low fever. Now?

What is the cause for  low fever I.e less than 100 in between 99-99.8,which tests are useful for detecting fever less than 100 suffering from 3 mnths ,earlier in this 3mnths period got thypoid and in thypoid also low fever o&h titre 1:160 after that titres reduced but still low fever ,done tests such as thyroid,smear mp,scrub thypus,Rh assay,urine normal,us abdomen normal,chest x-ray clear,I am vegetarian, less went outside will there any vitamin d deficiency,or b12 def? Vit d Or b12 blood tests are useful now?,Or which tests are useful now pls give the tests,doctors give suggestions don't keep chat or consult because iam asking about the low fever so which parameters will reflect this since from so many days asking no single doctor is ready to give answer,which blood tests are useful for me and which harmones are regulate temp for men pls give answer doctors