We all tend to blame fatigue on a too-busy lifestyle. And much of the time we're right. But if you feel tired all the time, don't blow it off. Give yourself about 2 to 3 weeks to make some lifestyle changes: Get more sleep, trim your social calendar, eat more wholesome foods, drink more fluids, take a multivitamin, and cut back on caffeine and alcohol. "If you're still feeling the symptoms of fatigue after those changes, then you need professional help. Excess exhaustion could be the sign of a more serious medical condition that can be treated. Here are some common problems you need to know about. 1. Anemia The fatigue caused by anemia is the result of a lack of red blood cells, which bring oxygen from your lungs to your tissues and cells. You may feel weak and short of breath. Anemia may be caused by an iron or vitamin deficiency, blood loss, internal bleeding, or a chronic disease such as rheumatoid arthritis, cancer, or kidney failure. Women of childbearing age are especially susceptible to iron-deficiency anemia because of blood loss during menstruation and the body's need for extra iron during pregnancy and breastfeeding. The symptoms: Fatigue is a major one. Others include extreme weakness, difficulty sleeping, lack of concentration, rapid heartbeat, chest pains, and headache. Simple exercise, such as climbing the stairs or walking short distances, can cause fatigue. The tests: A thorough evaluation for anemia includes a physical exam and blood tests, including a complete blood count (CBC), to check the levels of your red blood cells. It's also standard to check the stool for blood loss. 2. Thyroid Disease When your thyroid hormones are out of whack, even everyday activities will wipe you out. The thyroid gland, about the size of the knot on a man's tie, is found in the front of the neck and produces hormones that control your metabolism. Too much thyroid hormone (hyperthyroidism), and metabolism speeds up. Too little (hypothyroidism), and metabolism slows down. The symptoms: Hyperthyroidism causes muscle fatigue and weakness, which you may notice first in the thighs. Exercises such as riding a bike or climbing stairs become more difficult. Other symptoms include unexplained weight loss, feeling warm all the time, increased heart rate, shorter and less frequent menstrual flows, and increased thirst. Hyperthyroidism is most commonly diagnosed in women in their 20s and 30s, but it can occur in older women and men too. Other symptoms include weight gain due to water retention, feeling cold all the time (even in warmer weather), heavier and more frequent menstrual flows, and constipation. Hypothyroidism is most common in women over age 50; in fact, as many as 10% of women past 50 will have at least mild hypothyroidism. 3. Diabetes More than a million people are diagnosed with type 2 diabetes every year, but many more may not even know they have it. Sugar, also called glucose, is the fuel that keeps your body going. And that means trouble for people with type 2 diabetes who can't use glucose properly, causing it to build up in the blood. Without enough energy to keep the body running smoothly, people with diabetes often notice fatigue as one of the first warning signs, says Christopher D. Saudek, MD, professor of medicine and program director for the General Clinical Research Center at the Johns Hopkins University School of Medicine. The symptoms: Aside from exhaustion, other signs include excessive thirst, frequent urination, hunger, weight loss, irritability, yeast infections, and blurred vision. 4. Depression More than "the blues," depression is a major illness that affects the way we sleep, eat, and feel about ourselves and others. Without treatment, the symptoms of depression may last for weeks, months, or even years. The symptoms: We don't all experience depression in the same way. But commonly, depression can cause decreased energy, changes in sleeping and eating patterns, problems with memory and concentration, and feelings of hopelessness, worthlessness, and negativity. (These other9 unexpected symptoms of depression are less common, but just as telling.) The tests: There's no blood test for depression, but your doctor may be able to identify it by asking you a series of questions. If you experience five or more of these symptoms below for more than 2 weeks, or if they interfere with your life, see your doctor or mental health professional: fatigue or loss of energy; sleeping too little or too much; a persistent sad, anxious, or "empty" mood; reduced appetite and weight loss; increased appetite and weight gain; loss of interest or pleasure in activities once enjoyed; restlessness or irritability; persistent physical symptoms that don't respond to treatment, such as headaches, chronicpain, or constipation and other digestive disorders; difficulty concentrating, remembering, or making decisions; feeling guilty, hopeless, or worthless thoughts of death or suicide. 5. Rheumatoid Arthritis This autoimmune disease is not always easy to diagnose early, but there are some subtle clues to look for. RA happens when your immune system turns against itself and attacks healthy joint tissue, sometimes resulting in irreversible damage to bone and cartilage. The symptoms: Many symptoms (such as fatigue, low energy, loss of appetite, and joint pain) are shared by other health conditions, including other forms of arthritis such as fibromyalgia and lupus. Anemia and thyroid disorders, which also cause fatigue. Rheumatologists look for at least four of the following criteria in diagnosing RA: morning stiffness in and around the joints lasting at least 1 hour before maximum improvement; at least three joint areas with simultaneous soft tissue swelling or fluid; at least one joint area swollen in a wrist, knuckle, or the middle joint of a finger; simultaneous involvement of the same joint areas on both sides of the body; lumps of tissue under the skin; and bone erosion in the wrist or hand joints, detected by x-ray. The tests: A thorough physical exam by a rheumatologist can provide some of the most valuable evidence of the disease, but there is also a test for the presence of rheumatoid factor, an antibody found in the blood. About 80% of people with RA test positive for this antibody, but the test is not conclusive. 6. Chronic Fatigue This baffling condition causes a strong fatigue that comes on quickly. People who suffer from CFS feel too tired to carry on with their normal activities and are easily exhausted with little exertion. The symptoms: Other signs include headache, muscle and joint pain, weakness, tender lymph nodes, and an inability to concentrate. Chronic fatigue syndrome remains puzzling, because it has no known cause. The tests: There is none. Your doctor must rule out other conditions with similar symptoms, such as lupus and multiple sclerosis, before making the diagnosis. 7. Sleep Apnea You could have this sleep-disrupting problem if you wake up feeling tired no matter how much rest you think you got. Sleep apnea is a disorder characterized by brief interruptions of breathing during sleep. In the most common type, obstructive sleep apnea, your upper airway actually closes or collapses for a few seconds, which, in turn, alerts your brain to wake you up to begin breathing again. Someone with obstructive sleep apnea may stop breathing dozens or even hundreds of times a night. The symptoms: Sleep apnea is often signaled by snoring and is generally followed by tiredness the next day. Because sleep apnea can lead to heart disease, high blood pressure, and stroke, it's important to be tested.