If you're talking about two glands right under your chin (not farther back under the jaw) you could be dealing with swollen salivary glands. Sometimes the saliva becomes too thick to be secreted through the ducts. The glands are very reactive to various things that make you salivate and if the saliva can't flow they'll swell up. Also, something could be irritating the actual ducts, causing them to constrict and impede flow. Could be an infection. Alleviating this problem could be as simple as swishing warm water around in your mouth very hard several times a day. Best see a doctor just to check. If the swelling is farther back, under your jaw, it might be your lymph nodes, which can swell and unswell from almost anything.
Regards,
richard day gore