I realy don't get what's goin on with me sooooo please help

first of im black and really light skinned.
when im outside in the sun my body does get tanned so i turn somewhat darker. my forehead and gets darker too BUT my cheeks and the sides of my face (by my eyes) get lighter!! so i look weired!!!!

this happens on and off sometimes it lasts days, sometimes months.

I did see a dermatologist once, she prescribed this thing with steroid in it that did nothing.

so what is it? im pretty sure its not vitiligo cuz it disapears and its not acne.