Regarding the low grade persistent fever

Which produce  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 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?, 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 on practo,,will any one have 99-99.8 as a normal temp,on which which factors body temp changes,some new small black moles formed on body is it natural normal ,earlier my body temp 1yr back it is 97.6 ,why now it is 98-99.8 worrying about this iam lagging in my studies not able to concentrate on studies help doctors which blood tests are useful now??