Viral Pharyngitis: This is the most common cause of sore throat and is often accompanied by mild congestion and cervical lymphadenopathy. The absence of cough and the presence of posterior cervical lymphadenopathy support this diagnosis, as viral infections commonly cause localized lymph node enlargement.

Streptococcal Pharyngitis: Although less common than viral pharyngitis, streptococcal (strep) throat is a significant consideration, especially if the sore throat is severe, and there's a history of exposure to someone with strep throat. The presence of lymphadenopathy and the absence of cough are consistent with this diagnosis.
Mononucleosis (Infectious Mononucleosis): Caused by Epstein-Barr virus (EBV), this condition often presents with sore throat, significant cervical lymphadenopathy, and can include mild congestion. It's more common in young adults and can be considered if the patient has fatigue, fever, or other systemic symptoms.
Acute HIV Infection: This can present with a flu-like illness that includes sore throat, lymphadenopathy, and sometimes a rash. It's less common but should be considered in individuals with risk factors for HIV exposure.

Lymphoma: Although rare, lymphoma can present with lymphadenopathy, and a sore throat if there's involvement of the Waldeyer's ring. It's crucial to consider in the differential due to its significant implications for treatment and prognosis.
Tuberculosis (TB): TB can cause cervical lymphadenopathy and a chronic sore throat. It's essential to consider, especially in individuals with risk factors for TB exposure or those who are immunocompromised.
Lemierre's Syndrome: A rare but serious condition caused by Fusobacterium necrophorum, characterized by sore throat followed by cervical lymphadenopathy and sepsis. It's a medical emergency and requires prompt diagnosis and treatment.

Toxoplasmosis: Can cause lymphadenopathy, but it's less commonly associated with sore throat. It might be considered in immunocompromised patients or those with specific exposure risks.
Cytomegalovirus (CMV) Infection: Similar to mononucleosis, CMV can cause a sore throat and lymphadenopathy, but it's less common and typically seen in immunocompromised individuals or those with specific risk factors.
Syphilitic Pharyngitis: A rare cause of sore throat, associated with primary syphilis. It would be considered in individuals with risk factors for sexually transmitted infections.