Sore that stings in the back of my mouth?

I have a sore in the very back of the left side of my mouth. It's kind of on my cheek on the side of my tooth, it stings and hurts to chew on that side of my mouth. I thought it was nothing but now my boyfriend has it too. And it's also in the same exact place. I know that it's definitely NOT a canker sore so, don't tell me that. Thanks