The inside of the mouth (and especially under the tongue) is a clutter of bumps, ridges, discolorations and weird looking things. Most dentists do an "oral health exam", so if you're truly worried, call your dentist and tell the receptionist, "I feel a lump under my tongue and I'd like to see the doctor". A dentist will know precisely what to look for, and will quickly put your mind at ease. Also, the inside of the mouth is very sensitive, so you could have an irritated area (this often happens to me if I eat popcorn, or anything that is very crunchy like granola, chips, etc.). God Bless.