Monitoring your health is inseparable from monitoring your temperature. It is well understood in medicine and science that the body temperature will increase (fever) to help fight off infection.
But did you know that your core body temperature actually varies throughout the day. It is normal for your temperature to change naturally by about 1 degree Celcius over a day.
This normal variation in body temperature is called the Circadian Rhythm. Usually your temperature will decrease during the night and rise during the day.
So what you may have thought was the 'standard human body temperature' of 37°C (98.6°F) is an average. Furthermore, the Circadian Rhythm can vary between people along with their average temperature so it is quite individual.