Hello
It is due to the wisdom tooth that has partially erupted in the mouth. It is known as pericoronitis.
You will have to a Maxillofacial Surgeon and get it checked. Transient relief can be achieved by operculectomy , but if it troubles you repeatedly, then the wisdom tooth has to be removed.
You can do warm saline rinses thrice a day.
Next Steps
You can get in touch with us. We are a team of doctors ( Dr Rohit Yadav: Maxillofacial Surgeon and Implantologist; Dr Shivani Mangal: Endodontist) practicing in New Delhi
Health Tips
Don't rely on medicines. They are not going to help for long