Viral Pharyngitis: This is the most common cause of a scratchy throat and is often accompanied by fatigue and chills. It is usually self-limiting and caused by viruses such as rhinovirus, coronavirus, or adenovirus.

Influenza: Characterized by sudden onset of high fever, chills, and fatigue, often accompanied by a sore throat. It's a common condition, especially during flu season.
Mononucleosis (Mono): Caused by the Epstein-Barr virus, it can present with fatigue, sore throat, and fever. It's more common in younger adults.
Streptococcal Pharyngitis: Although less common than viral pharyngitis, it's a significant cause of sore throat and can be accompanied by fever and fatigue. It requires antibiotic treatment to prevent complications.

Epiglottitis: A potentially life-threatening condition that can cause severe sore throat, difficulty swallowing, and shortness of breath. It's less common but critical to diagnose early.
Lemierre's Syndrome: A rare but serious condition following a sore throat, characterized by fever, sore throat, and neck pain, which can lead to sepsis and embolic events.
HIV Acute Infection: The initial presentation of HIV can mimic a flu-like illness with sore throat, fever, and fatigue. Missing this diagnosis can have significant long-term consequences.

Toxoplasmosis: Although more commonly associated with neurological symptoms in immunocompromised patients, it can occasionally present with a mononucleosis-like syndrome in immunocompetent individuals.
Cytomegalovirus (CMV) Infection: Similar to mononucleosis, CMV can cause a prolonged illness with fever, fatigue, and sore throat, more commonly in immunocompromised individuals or those without prior exposure.
Tuberculosis (TB): While TB can present with a variety of symptoms, a chronic sore throat, fever, and fatigue could be part of its clinical picture, especially in individuals from endemic areas or with risk factors for TB exposure.