Suggest Treatment For White Spot On Face

hello doctor i m 23 years old girl.my weight is 50kg and height is 5f .there is white spot on my face from very long time.i tried many medi n cream declared by doctor but i hav no relief .please tell me what is the reason of it n what is the solution.doctors says that it is a sunburn. but if it is sunburn then why it take long time to cure????