Bottom of my tongue hurts when I stick it out?

Floor of mouth. When you extend your tongue out of your mouth, the structures in the floor of the mouth are stretched and if there is any inflammation in that space under your tongue (behind your lower teeth) pain will occur. An oral surgeon or specialist in oral medicine should be consulted. The floor of the mouth has sublingual glands, and a structure called the frenulum. If the frenulum is tight, it can hurt.