Help please with brown skin pigmentation?

There is a middle dip above the actual lip that kinda folds within the center above the lip. Well, in the center it appears to be darkened. The shape is a circle.This area is smaller than a pencil eraser but it shadows a lot, making it more prominent. It is a flat brown area that looks like a birthmark or hyper pigmentation. I've never had this before and suddenly appeared over 3 months ago. It is just a flat light to medium brown spot. I don't know if that could have caused my problem. Whatever it is, will not go away and it bothers me a lot. I'd just turned 15 yrs old; also, i have very pale skin so this pigmentation stands out. What is it and what can i do to treat it with fast results?