Hello.
Looks like your wisdom tooth is erupting and causing swelling in the surrounding area. food lodgement in the wisdom tooth area also might lead to such condition. It might get infected. So make sure you keep that area clean. Use floss to clean that area.
Next Steps
Visit your dentist for examination.
Health Tips
Do warm saline gargles and chlorhexidine mouthwash separately thrice a day, don’t eat hard things from that side. You may take some analgesic to get rid of pain.