Happens to the end of my tongue occasionally because I have a snaggletooth on the bottom front that sticks back. Then I keep “feeling” it with the end of my tongue and irritate it.I've never gotten "pimples" inside my mouth, but I get canker sores a lot inside my bottom lip from my canine tooth. I think it's from smoking, based on how my lips touch my teeth either with a cigarette or my pipe . She's a sharp one.