I have a piece of gum that is extended over my very back tooth i can get under it with my tongue and move it up and down and it hurts. irritated!

See a dentist: If you have a wisdom tooth (18 year molar), under that gum, it may need to be removed as you are 21 years old. If the wisdom tooth has been removed, then you have overgrown gum tissue that can be easily removed by your dentist using a soft tissue dental laser. See your dentist soon to reduce the chance of infection.

Remove it: You need to have that coronal portion of the gum that goes over the top chewing surface of the tooth removed for better function and eliminate potential infections from foods and plaque accumulation under it.

Wisdom tooth: Try warm compresses. Wisdom teeth typically come out after age 17 ; can be stuck ; painful. You may need to have it taken out. See dentist to be sure.

Pericoronitis : Is an infection near wisdom tooth. Sometimes, there's not enough room for them, and they come in partially or not at all. This condition can lead to pericoronitis, inflammation of the tissue surrounding the tooth. Pericoronitis is diagnosed during a clinical exam by your dentist. Rec.: see your dentist for further investigation. Sometimes no treatment is the best treatment.

Pericoronitis: There is probably not enough room in your jaw for your wisdom tooth. An xray should tell if there is a possibility that it could continue to erupt fully without further complications. At your age, i would expect you will need to have the wisdom tooth extracted in order to fix the problem.