Thanks for your query.
As you provided the detail,it seems that this is your wisdom tooth which is erupting and covered with gum tissue.
First of all i would like to tell you that wisdom tooth eruption
is painfull up to a some extant and this area is not easy to clean because of that remaining food particals results in inflammation in that area and become pain ful.
So i will suggest you please visit to an oral surgeon as soon as possible and get the thorough examination done including x-ray of that tooth.
After all these things take a proper treatment accordingly,if there is sufficient space for its eruption,you can remove that flap over this tooth.
If not you can go for this tooth extraction.
Mean while maintain good oral hygiene
,rinse your mouth with warm saline ,rinse your mouth after each meal.
Nothing to get worried.
Dr. Gunjan Gupta