I have a little bubble under my tongue and i don't know what it is?

Oral mucocele: is a benign condition and it can happen when a salivary gland is injured or blocked. However, it's still a good idea to get it checked out, though, especially if it's bothersome. See your dentist for evaluation.

Mucocele/ranula: Probably a salivary gland cyst; saliva is being produced but the duct that drains the saliva into the mouth is clogged and so it swells like a balloon. Usually resolve on their own.

Possible Ranula: A ranula presents as a fluid filled bubble on the floor of the mouth under the tongue. It is caused by a blocked salivary gland. The saliva can't get out so it backs up and creates a bubble. Small ranulas can often resolve on their own. Larger ones (shown here) may require surgical removal.