Pimples inside mouth???

Well i have heard that is a bunch of like mini pinsize pimples in a small area but for the past like couple of months id have random single pimples in my mouth like ill have one of my like left cheek by my mouler and like one in front of my bottom left lip. what could that be getting them teredly but steadily from week to week they are never like two in one spot. thats what i dont understandd.