What is the cause of a painful lump along the right jaw line and under the ear, with intermittent pain?

Lymphadenitis or Lymphadenopathy: This is the most likely diagnosis due to the location of the lump (right jaw line and under ear) and the symptom of pain. Lymph nodes in this area can become inflamed or enlarged due to infection, which would cause intermittent pain.

Dental Abscess or Infection: Infections of the teeth or gums can cause pain and swelling in the jaw area, potentially leading to a palpable lump under the ear or along the jaw line.
Parotid Gland Disorders: Conditions affecting the parotid gland, such as parotitis (inflammation of the gland) or a parotid cyst, could present with a lump and pain in the area under the ear.
Submandibular Sialadenitis: Inflammation of the submandibular gland can cause swelling and pain under the jaw, which might be perceived as a lump.

Malignancy (e.g., Lymphoma, Metastatic Cancer): Although less common, it's crucial not to miss a potential malignancy, such as lymphoma or metastatic cancer to the lymph nodes, which could present with a painless or painful lump.
Tuberculosis or Atypical Mycobacterial Infection: These infections can cause lymphadenopathy and might not be immediately suspected but are critical to diagnose due to their treatment implications.
Cat-Scratch Disease: Caused by Bartonella henselae, this infection can lead to lymphadenopathy, typically after a cat scratch or bite, and is important to consider in patients with a history of animal exposure.

Branchial Cleft Cyst: A congenital anomaly that can present as a lump along the side of the neck, which may become infected and painful.
Actinomycosis: A rare bacterial infection that can cause chronic abscesses or masses in the jaw and neck area, often associated with poor dental hygiene or oral trauma.
Kimura Disease: A rare, chronic inflammatory disorder that can cause lymphadenopathy and eosinophilia, typically presenting with a subcutaneous mass in the head or neck region.