yes, it is common for me to have low grade fever, I can tell if it is from my acid reflux meds (low grade fever is one of the many side effects of acid reducer meds). And I can certainly tell if it is from my fibro because it would feel like I am going down with flu but it would only last a day, then recur after several days or weeks. The last time I visited my doc I mentioned this to her, but when the test results came back it was negative for any infection.
Oddly enough, my body temperature varies from hour to hour!