the core temp thing isn't a lie for some people.  See, I wondered about that and know that it's plausible. But if your temp is within range it's not a fever. So one degree above whatever your normal is is usually not considered a fever - by most standards and what pediatricians always told me.  Besides, if every time you take your temp, it's 98.6 and you've taken your temp ~10 times over the last 3 months, wouldn't that kinda establish a baseline of 98.6 and not a fever of 98.6?