I saw something on this very recently, but I can’t recall where. It had to do with some contaminant in certain lipsticks. (It’s not a joke that I really saw this, but I can’t be certain that the posting that I saw was honest / accurate / serious.)
If I can find it again I’ll post a link.
EDIT: Okay, I haven’t found the exact post that I glanced at (not being a lipstick wearer, and without a current main squeeze, I don’t read all of the ‘girl-directed’ articles that I run across – unless they’re about “her”), but I recall the topic now: Lead in Lipstick.
If you google that term you’ll find a lot of conflicting information regarding how lead can cause black lips in cheap, low-quality (non-compliant with FDA regulations) lipstick, and other sites claiming to “bust that hoax, because such cosmetics would never be allowed in the USA”.
Wherever the truth lies, it might be a good idea to check out the cosmetics that you are using, and maybe not use them for awhile, and see if that helps. It’s not as if you need lipstick to make it through the day, do you?