I don't trust digital thermometers. They often do not go below 97F, so I would get a glass thermometer instead. Here is a partial write I have for the thyroid that explains it:
A more accurate way to determine if the thyroid is low is to do a procedure known as basal body temperature. To perform this procedure you'll need a glass thermometer. S hake the thermometer down before you go to bed, and place the thermometer on your nightstand. When you first wake up in the morning reach over and grab the thermometer. Place the thermometer under your armpit for 10 minutes holding your arm against your body. Read the temperature, and write the temperature down on a log. Do this first thing in the morning for at least one week. It is very important that you do not get up or move around before taking your temperature. Getting up or otherwise moving around will raise your body temperature due to muscle heat, which leads to a false reading. Your temperature should read at least 97.6 degrees Fahrenheit each morning
A lower reading down to 97 degrees Fahrenheit indicates mild hypothyroidism. A reading below 97 degrees Fahrenheit indicates more severe hypothyroidism. Note that menstruation alters the body temperature, which creates false readings. Therefore, I recommend taking the basal body temperature for one to two weeks to get a good average.
An underactive thyroid can result in symptoms other than low body temperature. In addition, a person may have one or more of the following symptoms. Weight gain, goiter, dry and thick skin, thickened nails, falling hair (especially in women), low energy, slow heart rate, memory problems, cold intolerance, cold hands and feet or, constipation, low sex drive, memory problems, depression, infertility and heavy menstruation.
Another, and often overlooked, side effect of low thyroid function is a greatly increased risk of heart disease. One role of the thyroid is in the metabolism of fats, including cholesterol. Compounding this problem is the fact that low thyroid function also increases levels of the inflammatory compound homocysteine. Increased homocysteine levels in turn increase inflammation of the arterial walls, which leads to depositing of cholesterol on the arterial walls.
The autoimmune disorder Hashimoto's thyroidosis was once considered to be a rare condition. Now Hashimoto's thyroidosis is considered, by some, to be the leading cause of hypothyroidism. Diagnosis of Hashimoto's thyroidosis is generally made by the findings of elevated TSH, and low T3 and T4.
If you find that you are hypothyroid let me know and I can direct you to more information.