Why do i keep getting dandruff on the left side of my head?

Okay i am african american so i kno i dont have lice but i keep getting dandruff just only on the left side of my head. I wash my head all over and oil it with grease and in about three days only the left side get dandruff this been going on for a year even when i use sulfur 8 and bamm in like 3 days the flakes are back just on the lower left side of my head in the front why?