Hi.. Thanks for the query.. Well, a bubble like lump under the tongue can be most probably a Mucocele that occurs due to obstruction in the duct of the minor salivary gland.. Nothing to worry as it is self limiting and resolves on its own.. You can do salt water rinses as it helps in shrinking the bubble like lump faster.. In case if it continue to get painful then it can probably be an abscess caused due to infection and in that case you need to consult an Oral Physician and get evaluated so that they can lance the lump and drain of its contents and advise you antibiotics.. But first of all you should do salt water rinses and watch.. Hope this helps.. Regards..