what you have on your lip is a birth mark. it is a form of benign hyperpigmentation
as of your teeth it must be something you are eating like roasted food etc.
if you are. brush your teeth twice a day. look out for high flouride in the water you consume.
look out for hyperpigmentation on your palms and feet. get a general health check done. rule out history of hyperpigmentation in your family. if this continues or becomes worse contact your physician regarding the same.
i hope i have answered your query.