This skin discoloration is due to melasma. It is caused by hormonal changes, which stimulate a temporary increase in your body's production of melanin. People with darker complexions are more prone to this condition than people with lighter skin.
Treatment options include treatment with vitamin C and hydrocortisone, peel with carbon dioxide snow and alexandrite and ND-Yag Q-Switched laser treatment preceded by a hydroquinone-based application. Please discuss these options with your dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.