How To Get Rid Of Skin Pigmentation On Face?

I have lot of pigmentation on my face from last 7 years but it worsened from last 2012.i am on antidepressant amitriptyline and chorodiazepoxide from last 8 years. I applied of medicines but nothing worked out. Before few years my skin was flawless and 2 months back I consulted the dermatologist and he suggested to apply it for 3 months. There is slight improvement but not much, so what do you suggest