You should visit a doctor as soon as possible and get your mouth checked. A lump under the tongue can be many things, but one possibility is cancer. It is best not to waste time conjecturing and trying home remedies when cancer is a possibility, as any delay in detection and treatment can have major consequences. You should go for a check up immediately, so that if the lump is cancerous, you can begin treatment. The symptoms you mention — a lump, pain, and difficulty swallowing — are all symptoms of oral cancer.
Other possibilities include a benign tumor, an oral mucocele, Sjogren's syndrome, and salivary gland stones. A mucocele occurs when a salivary gland duct is ruptured as a result of trauma. No treatment is required unless the condition seems to be chronic, in which case minor surgery may be necessary.
Salivary gland stones sometimes develop, causing swelling and pain. While this is a minor condition, you will need a doctor to remove the stones, as well as for diagnosis. Sjogren's syndrome is an autoimmune disorder that sometimes affects the salivary glands, however this is unlikely as the symptoms of this disorder include dryness of the eyes and mouth, neither of which you have mentioned.
answered by G M