i can understand your concern.
i would recommend that you stop the melalite cream..
first of all, the most important thing to prevent darkening of skin is to prevent constant sun exposure by using a sunscreen of SPF more than 50 if possible. this has to be applied on all exposed parts half an hour before going out to sun and reapplied every 4 hours.
a daily regimen of cleansing your face thrice a day, moisturizing and using sun screen is very effective.
also application of glycolic acid
6 % cream will help in resolving the marks. it has to be applied at night daily.