There are many reasons why your skin would turn dark. Sun tan, overweight, pigmentation disorders like acanthosis or melasma, nutritional deficiency etc are some conditions. Unless someone examines you, we cannot know the cause. Unless we find out the cause it is difficult and pointless to treat. Please call me or send photos with detailed history using online consult option for proper treatment.

This is limited information and tells nothing about your skin condition which can help in planning a treatment.  A thorough history, clinical examination and appropriate laboratory tests will be needed to solve the mystery. Consider seeing a Dermatologist for proper diagnosis and treatment plan.