There are a few things it could be, but if it's not dental in origin, and it's not a swollen lymph gland, then it could be a stone that's formed in a salivary gland.

These stones aren't uncommon and they're called Submandibular (or submaxillary gland) Salivary Gland stones, and can be very painful.

Here's some links that explain a bit about them, but there's plenty more on the Net if you want to do a search.
http://www.patient.co.uk/health/Sali...and-Stones.htm

http://www.allhealth.com.au/html/s02...tory=2&cr=true

I know this may not be the answer to your problem but if it is a stone, they often fix themselves. Please feel better soon.