Based on the history and photograph, this appears to be pericoronitis associated with a partially erupted wisdom tooth. Food accumulation and bacterial infection beneath the gum flap commonly cause pain, swelling, and difficulty in chewing.
Next Steps
Maintain good oral hygiene, rinse gently with warm saline water, and avoid chewing on the affected side. A clinical examination and X-ray (OPG) are required to assess the position of the wisdom tooth and determine the need for further treatment, including possible extraction after the acute symptoms subside. If you develop severe swelling, fever, difficulty opening the mouth, or difficulty swallowing, seek dental care promptly.”