To be honest, many nepalis do not know how to brush teeth properly. And they do not brush after dinner at night. Use dental floss to get the dirt out from teeth. Use sensodyne if your teeth are sensitive. You can use Listerine to mouthwash regularly. The way to brush is up and down and not horizontally. And brush back and forth to get the dirt out from inbetween the teeth.

Apply cold pack to the area. IF you already did all and does not heal then visit a dentist. :). Proper dental care means in old age you will not need dentures. :)