welcome to healthcare magic forum .
thank you for your query .
hyper pigmenatation is due to many reason .
it may be heredity ,diet related ,drug induced ,allergic ,low hb ,thyroid disease
it is better to find out the reason first .
good sun screen is best option to prevent further damage
in your case you should go with your dermatologist
do not use it for more than 4 weeks
i hope i answered your query .