[Routine Help] Now that my acne has stabilized, I'd like to start working on fading dark spots. How do I incorporate Vitamin C or lactic acid in my routine?

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I've got somewhat sensitive skin, and had horrible acne from an IUD (has since been removed) and stress. In the past 8 months, I've stuck to a very simple but great routine getting the acne under control. And I'm so happy with the results! But I have a lot of dark spots left that I'd like to fade. Since my routine is pretty simple, I think it'll be relatively easy to work in Vitamin C or lactic acid, but I'm not sure which I should start with, which brand/product to use, and how to integrate it. I'm a little overwhelmed by the wiki info, and having a hard time figuring out how to adjust my routine to make it happen. Here's my routine:AM:Cerave washCerave AM moisturizer w/SPFPM:Cerave washThe Ordinary Niacinamide and ZincCerave PM moisturizer​My skin can get dry pretty easily, and I'm in New England, so it's approaching the worst time for dry skin, so I want to stay on top of keeping my skin moisturized.picture of spots
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