Do you have those inside your mouth or ...esp in gums?
It sounds like dark Pigmentation. Check your lipstick to see if it has specific oils in it that might interact with the sun and cause skin discoloration. The best treatment for the dark spots would be GLYCOLIC treatments. If they are too expensive for you, then I would get a good acid cream from your Dermatologist. It should fade but it might take a while. If you don't do anything about it, trust me when I say that it will definitely get darker and bigger and I'm sure you don't want that. O.K. gOOD lUCK