What could cause your fever to fluctuate when it runs normal around 97 during the day but in the evening and at night it raises sometimes to 100 or slightly over?

Allergies can make your temperature go up so you may be allergic to something in your home. Carpeting, fresh paint, some woods, soaps, PMS, perimenopause, menopause, etc., are some culprits. Although 100 degrees sounds high it isn't all that high. If we were to check out our temperatures, blood pressure every hour on the hour during the day we would be shocked to see how much it fluctuates and it depends on the stress level or exercise we may be getting during the course of that day. 98.6 degrees is the correct temp. for humans, but it doesn't always stay there during a full day. See your doctor and have a T3/T4 blood test done on your thyroid and let the doctor know the fluctuation in your body temperature. It probably isn't anything serious, but having a doctor explain things to you will put your mind to rest.