I woke up and under my tongue is swollen I don't know why?

See your dentist. You should have this checked immediately. It is probably a minor problem, but could be caused by a clogged salivary duct or other less common reason.
Get it checked. There can be many reasons for swelling under the tongue. It could be as simple as a sensitivity to something you eat or drank, from a dry mouth, or something more. If it has not subsided within the next 24 hours you should be seen by a dentist or physician to fully evaluate the area.