Your wisdom tooth is erupted but the gum flap over it has failed to recede down. Because of this gum flap present, food debris and plaque tend to get entrapped between this gum flap called operculum and the tooth crown. Even with best brushing habits and gargling, debris and plaque are not removed as they are protected by the operculum. Long term accumulation results in booming of anaerobic bacteria causing swelling, pain and may be pus discharge. Also, the presence of upper wisdom molar worsens the condition by pressing on this operculum while biting.
Treatment:
The tooth should be examined clinically and an X-ray should also be taken. Many a times the tooth is covered with a thick gum flap and mucosa from the cheek. In such situations, surgical removal of operculum may not help and add to the problems, in such cases it is better to extract the tooth once the symptoms subside. But if your wisdom molar is completely erupted and has movable operculum on it, the operculum can be excised with a blade, electrocautery or a dental laser, very easily. The dental specialist who is best at solving this problem of yours is called Periodontist. Look for a periodontist around or ask your dentist to have your consultation with a Periodontist.
This is my article on wisdom teeth. U can use the link to read it.
https://www.google.co.in/amp/s/www.practo.com/healthfeed/amp/wisdom-teeth-unfolding-facts-and-myths-31239/post
Next Steps
Treatment of acute symptoms-
1) See a dentist
2) the dentist after clinical examination and X-ray, will give u slight Local anaesthesia to numb that tissue.
3) the dentist will clean out any debris n plaque underneath the operculum.
4) irrigation with saline and betadine
If u have pus discharge and lymph node swelling, then antibiotics may be required
Mouthwash for home use and an analgesic and anti inflammatory.
After symptoms subside, further treatment can be done.
Health Tips
U can do warm salt water gargles for some relief.