You might be talking about your wisdom tooth.and the growing skin is operculum which may be partially covering your teeth as your last tooth is not completely out or in occlusal line.infection would have started because of food Impaction in that region ,causing you pain.
Next Steps
visit a dentist and get x-ray done w.r.t that tooth.
Health Tips
warm saline rinses
otc painkiller for pain
clean the area nicely so that food lodgement doesn't happen