Thanks for asking the query,
Trauma and irritation on the side probably had caused accumulation of healing tissues and cells in the area resulting in formation of cyst
or little beningn fibroma
The area is difficult to clean so it often invites bacterial infection leading to redness
, inflammation , swelling of adjacent tissues.
Take care that it does not get infected.
Maintain a good oral hygiene.
take saline water gargles .
mouthwash gargles twice daily.
It is wise to consult to an Oral and Maxillofacial Surgeon and get a checkup done.
Hope this helps out.