Skin Has Turned Darker, Rapid Changes In Skin Color. Remedial Measures?

hi, this is pankaj from Goa i have a query for skin related problem,i m basically from north and since from last 6 years i m working in goa,earlier my skin was very fair but now these days i m finding that my skin turning toward darker complexation.at my working place i m working under air conditioned building and while going to office also i travel through my car So, hardly i get exposure of Sun, but eventhough very rapidly i m oberserving changes in my skin color,So, i need some remedial for this in form of tonic or oral solution,which can help in reducing melanin pigment in my body or some suggested diet plan or creams to apply on skin.pls. help and suggest.