Infectious Mononucleosis (Mono): Caused by Epstein-Barr virus (EBV), this condition is characterized by fever, lymphadenopathy, and fatigue, making it a common and likely diagnosis in patients presenting with these symptoms.

Tuberculosis (TB): A bacterial infection that can cause fever and lymphadenopathy, especially in individuals who have been exposed to TB or have a weakened immune system.
Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with fever and lymphadenopathy, and are important considerations in the differential diagnosis.
Influenza or Other Viral Infections: Seasonal influenza and other viral infections can cause fever and lymphadenopathy, particularly during peak viral seasons.

HIV Infection: Acute HIV infection can present with fever and lymphadenopathy, and it is crucial to consider this diagnosis due to its significant implications for patient management and public health.
Cat-Scratch Disease: Caused by Bartonella henselae, this infection can lead to fever and lymphadenopathy, especially in individuals who have been scratched by a cat.
Lymphogranuloma Venereum: A sexually transmitted infection caused by Chlamydia trachomatis, which can cause fever, lymphadenopathy, and other systemic symptoms.

Castleman Disease: A rare disorder that can cause fever, lymphadenopathy, and other systemic symptoms, often associated with lymphoproliferative disorders.
Kikuchi-Fujimoto Disease: A rare, self-limiting condition that presents with fever and lymphadenopathy, more commonly seen in young women.
Sarcoidosis: An autoimmune disease that can cause fever, lymphadenopathy, and other systemic symptoms, although it is less commonly associated with these specific symptoms compared to other manifestations like pulmonary involvement.