Thyroid problems
Although not as common a cause of fatigue as lifestyle issues, an underactive thyroid produces a number of symptoms, among them fatigue. When your thyroid is not producing enough hormone, your whole system slows down, which can lead to a number of health issues.
What to do: If your fatigue is not remedied by simple lifestyle changes, you should advise your doctor, who will likely want you to undergo a blood test. Once diagnosed, underactivity of the thyroid can be easily remedied by drugs.
Other health conditions
Other health condition that may give rise to fatigue include Chronic Fatigue Syndrome (CFS), fibromyalgia, and diabetes.
What to do: If you advise your doctor that you are chronically fatigued, he or she will likely arrange for a physical work-up which should lead to a diagnosis. Many medical conditions that cause fatigue can be successfully managed with a combination of lifestyle changes and/or prescription drugs.