If your tonsils are infected, it can cause a swelling in the lymph gland.
If you have popcorn stuck under a tooth or crown, and its abcessed, it can cause a swelling
If you have an old tooth with a root canal, they may not have dug far enough to remove all the old material, and it may have re infected.
You may have a new rooted abcess.

Do you have a water pik? wash out that area really well to make sure that no food debris is hung up. it will also massage the gums.

Do you have pain still? If so, your dentist needs to do an xray to check for leaking roots, or abcesses. it sounds like your lymph gland is telling you something in your mouth isnt happy. Even with no pain, the dentist needs to make sure its lymph, and not a bone protrusion that would mean something totally different.

Good luck