I'm kinda new to this so please take what I'm saying with a grain of salt, but for your PIH, I'd suggest The Ordinary. They have higher percentage ascorbic acid solutions which you may need as you're saying that the percentage you're currently using isn't working. When it comes to dullness, I like to DIY a physical exfoliator with honey and ground oats. I know a lot of people are totally against non-chemical exfoliation, but this one is super gentle, moisturizing, and of course supports bees! And if you're skin is still dry after everything, try a moisturizer like CeraVe that includes ceramides, which are a family of lipids found in human skin (and I think hair). They'll rehydrate your skin in no time. Good luck!