M.D.
I had the same thing. I finally went to the doctor when my child was two. It's a "pregnancy mask." I don't remember what the official name is, but my doc prescribed a bleaching cream that worked wonders. I had it on my lip, chin and cheeks. I urge you to consult your doctor. I know that when I use the cream I can't go in the sun. I use sunblock on my face whenever I leave the house. It's treatable and you'll feel "normal" again.