What could cause painful swelling in back of gums?

Inflammation ?: Infection? Those conditions can certainly cause swelling and pain. To determine exactly why your gum is swollen, you'll need to see a local dentist who can examine you. Together with a radiograph, they'll be able to make the proper diagnosis and treat you.

Wisdom tooth: A wisdom tooth that has not fully come in can cause a painful infection. This is an infection called pericoronitis and it needs to be examined by a dentist.