A low body temperature is usally associated to underactive thyroid, your thyroid gland doesn't produce enough of certain crucial hormones.
If you do have underactive thyroid, you should have some of these symptoms.
Increased sensitivity to cold
Elevated blood cholesterol level
Muscle aches, tenderness and stiffness
Pain, stiffness or swelling in your joints
Heavier than normal or irregular menstrual periods
Slowed heart rate
Enlarged thyroid gland (goiter)
However, there's a rare condition when people have low body temperature but normal thyroid hormones. It's called Wilson's Syndrome.