Dental infection or abscess: Given the recent tooth extraction 3 weeks ago, it's plausible that the lymphadenopathy is a response to a localized infection. The body's immune response to the infection could lead to swelling of the lymph nodes in the cervical region.

Viral pharyngitis: Common viral infections such as mononucleosis or other viral pharyngitides can cause cervical lymphadenopathy. The history of a recent dental procedure might not be directly related, but the timing could coincide with the onset of a viral infection.
Bacterial pharyngitis: Similar to viral causes, bacterial infections like streptococcal pharyngitis can lead to lymph node enlargement in the neck.
Reactive lymphadenopathy: This is a non-specific response to infection or inflammation elsewhere in the body, which could be related to the dental procedure or another concurrent infection.

Lymphoma: Although less common, lymphoma (Hodgkin's or non-Hodgkin's) can present with bilateral cervical lymphadenopathy. It's crucial to consider this diagnosis to ensure timely intervention if present.
Tuberculosis (TB): TB can cause lymphadenopathy, and although its incidence is lower in some regions, it remains a critical diagnosis to consider due to its implications for public health and the need for specific treatment.
HIV infection: Acute HIV infection can present with lymphadenopathy among other symptoms. Given the potential for severe consequences if left untreated, it's essential to consider HIV in the differential diagnosis.

Sarcoidosis: This autoimmune disease can cause lymphadenopathy, among other systemic symptoms. While less common, it should be considered in the differential diagnosis, especially if other symptoms or findings suggestive of sarcoidosis are present.
Kikuchi-Fujimoto disease: A rare, self-limiting condition that can cause cervical lymphadenopathy, typically in young women. It's an important consideration in the differential diagnosis due to its distinct presentation and benign course.
Castleman disease: A rare disorder that can cause lymphadenopathy, among other symptoms. It's essential to consider this in the differential due to its potential for significant morbidity if not recognized and treated appropriately.