large black mark on the lip

i have the habit of peeling my lip skin, i've been doin that for years , as the new skin grows i peel it off, jus can't help it and now i've got a large black mark on my lower lip, it started off as a purple discolouration a month ago then developed into a black colour mark n now it seems to be spreading to my upper lip; i wonder if it is a fungal infection or wat is it?, plz tell me wats happening [the cause] -i've told everything i know, n plz tell me the cure...........its gettin worse , i dont want my lip to become completely black by any chance.