Do you know what your average body temperature is? 98.6 is only an average and not a particularly accurate one. The original study about it was flawed. Some people naturally "run hot" or "run cold." Also, a woman's body temperature naturally spikes during ovulation leading up to her period.

It's mainly talked about for trying to conceive, but daily tracking of basal body temperature (your temperature before you get out of bed) is very useful for women to understand their menstrual cycles.

I always had the feeling I tend to run a little cold and tracking my temperature confirms it. My average temperature is closer to 97 degrees than 98 degrees. Knowing this, I know to be more concerned than most if my temperature goes above 98 degrees, because that's a higher fever than would be expected if you're assuming 98.6 as an average.

There could be something else going on, but if your temperature tends to average a little high, a temperature of about a hundred is still concerning but a higher average temperature would mean it's a less severe fever than you think. It's definitely still concerning if it's a sustained high temperature and if there are other symptoms. I think normal variation throughout the cycle should be talked about a lot more though so I took the opportunity.