Viral Pharyngitis: The patient's complaint of jaw pain and swollen glands radiating under the right ear for 3 days is suggestive of a viral infection, such as mononucleosis or a common cold, which often presents with lymphadenopathy and pain in the jaw and throat area.

Dental Abscess or Infection: Tooth infections can cause referred pain to the jaw and ear, along with swelling of the lymph nodes in the neck.
Sinusitis: Inflammation of the sinuses can cause pain in the face, including the jaw, and may lead to swollen lymph nodes.
Temporomandibular Joint (TMJ) Disorder: TMJ disorders can cause jaw pain and may be associated with swelling in the lymph nodes if there is an inflammatory component.

Lymphoma: Although less common, lymphoma can present with lymphadenopathy (swollen lymph nodes) and should not be missed due to its serious implications.
Parotid Gland Tumor: Tumors of the parotid gland, whether benign or malignant, can cause swelling in the area of the jaw and ear, along with pain.
Mastoiditis: An infection of the mastoid bone in the skull can cause pain behind the ear and jaw, along with swelling and is a serious condition that requires prompt treatment.

Sialadenitis: Inflammation of the salivary glands can cause pain and swelling in the jaw area but is less common compared to other diagnoses.
Osteomyelitis of the Jaw: A bone infection in the jaw can cause severe pain and swelling but is relatively rare.
Neurogenic Tumors: Tumors originating from nerve tissue can cause pain and swelling in the jaw and ear area but are uncommon.