Adolescent Sleep Deprivation: This is a common issue among teenagers due to a combination of factors including school schedules, extracurricular activities, and the natural shift in sleep patterns during adolescence, leading to insufficient sleep.

Anemia: Iron deficiency anemia is a common condition in adolescents, especially if they have a poor diet or increased requirements due to growth spurts, leading to fatigue.
Depression: Early signs of depression can include persistent fatigue, changes in appetite, and sleep disturbances, which are often overlooked in adolescents.
Mononucleosis (Mono): Caused by the Epstein-Barr virus, mono can lead to prolonged fatigue, sore throat, and fever, commonly affecting teenagers.
Hypothyroidism: Although less common, hypothyroidism can cause fatigue, weight gain, and dry skin, and its onset can occur during adolescence.

Diabetes Mellitus: Both type 1 and type 2 diabetes can present with fatigue among other symptoms like increased thirst and urination. Missing this diagnosis can lead to serious complications.
Sleep Apnea: Though more common in adults, sleep apnea can occur in adolescents, especially if they are overweight, leading to significant daytime fatigue.
Chronic Fatigue Syndrome (Myalgic Encephalomyelitis): A condition characterized by extreme fatigue that cannot be explained by any underlying medical condition, it's crucial not to miss this diagnosis as it significantly impacts quality of life.
Addison's Disease: A rare disorder of the adrenal glands, Addison's disease can cause fatigue, weight loss, and changes in skin pigmentation. It's life-threatening if not treated.

Mitochondrial Myopathies: A group of disorders that affect the mitochondria, leading to muscle weakness and fatigue. These are rare genetic conditions.
Wilson's Disease: A genetic disorder that leads to copper accumulation in the body, causing liver, neurological, and psychiatric symptoms, including fatigue.
Chronic Lyme Disease: If the boy lives in an area where Lyme disease is common and has been exposed to ticks, chronic Lyme disease could be a rare cause of his fatigue.
Cystic Fibrosis: Though typically diagnosed in childhood, some cases may not be identified until adolescence, with fatigue being one of the many possible symptoms due to chronic infection and malabsorption.