My dog, Bear, suddenly grew this swelling around March 5th.
It was a small bump the first day (Monday), then grew later that night (photo #1)
Throughout the week, it would grow and shrink - last night it grew to the biggest it has been (photo #2).
We changed his food last week to Nutro Natural Choice, he lives with another older dog and cat - in which, they all get along. The swelling is like a bruise - doesn't hurt with a light touch, but does with pressure. We think it's an abscess tooth or a bite from a bug.
We're gonna have to eventually take him to the vet if it doesn't get better - we just don't know much, it came out of nowhere.