What Causes Pigmentation Of Facial Skin On Exposure To Sun?

sir, my face skin started change to black when i be in sun light even for half an hour. So, i shown to skin specialist & professor in vijayawada Dr.P.Rambabu. Some blood tests were done & declared facial mellius. Since than i am using Ensoft 200mg.tab daily & applying sunburn & skin lite, since 15months. Inspite of which my face getting black patches & same problem continuing. What is the parmanent remedy. I am aged 32 yrs, unmarried & working as computer operator . Please prescribe me the best