Parotitis: This is the most likely diagnosis given the symptoms of pain and swelling in the parotid region. The ultrasound findings of benign-appearing lymph nodes within the parenchyma of the right parotid gland and the absence of suspicious masses or stones support this diagnosis. The normal appearance of the gland after stimulation with a sour candy also points towards an inflammatory process rather than a obstructive one.

Sialadenitis: This is an inflammation of the salivary glands and could present with similar symptoms. The ultrasound findings do not specifically point to sialadenitis, but it remains a consideration given the clinical presentation.
Lymphadenitis: Inflammation of the lymph nodes within the parotid gland could cause pain and swelling. The presence of benign-appearing lymph nodes supports this possibility, although it is less specific than parotitis.
Viral infection: Viral infections such as mumps or parotid gland involvement in other viral illnesses could present with similar symptoms. However, the absence of systemic symptoms or specific ultrasound findings makes this less likely.

Parotid gland tumor: Although the ultrasound did not show suspicious masses, it is crucial not to miss a potential tumor. Tumors can sometimes have a benign appearance, and clinical correlation along with potentially further imaging or biopsy might be necessary.
Sjögren's syndrome: An autoimmune disorder that can affect the salivary glands, leading to inflammation and potential swelling. This diagnosis is important not to miss due to its systemic implications and the need for specific management.
Lymphoma: Although rare, lymphoma involving the parotid gland or its lymph nodes is a critical diagnosis not to miss. The presence of lymph nodes, even if they appear benign, warrants careful consideration of this possibility.

Sarcoidosis: A systemic disease that can affect multiple organs, including the salivary glands, leading to inflammation and swelling. This would be an unusual presentation but should be considered in the differential diagnosis of parotid gland swelling.
Granulomatous disease: Conditions like tuberculosis or granulomatosis with polyangiitis can rarely affect the parotid gland, leading to its inflammation. These diagnoses are rare but important to consider in the appropriate clinical context.
Parotid gland cyst: A benign cystic lesion within the parotid gland could cause swelling and pain. The ultrasound did not specifically identify a cyst, but this remains a possibility in the differential diagnosis.