I have a swollen spot under my tongue close to the back side of my teeth. it is sore. what could it be?

See your dentist: I would have it evaluated by your dentist or primary care physician. A minor infection on the tongue, tooth abscess or a swollen salivary gland is not uncommon and can cause pain and irritation. The proper diagnosis is the key to a successful treatment. See your dentist for evaluation and diagnosis.

It's possible: maybe its a thyroglossal duct cyst. Its only a thought but check it out with your family doctor.