You seem to have melasma which happens because of harmonal changes the greatest enemy for that is the UV light. So use a good quality sunscreen...it's better to get yourself examined by a qualified dermatologist.

Thanks for the query. It is not possible to make a diagnosis based on the limited description of your problem and no photographs. Most likely diagnosis could be a skin condition known is "Melasma" which cause brown patches on cheeks/ nose. I would suggest you to see a Dermatologist for proper evaluation and appropriate treatment based on correct diagnosis.