Uff, pregnancy does so much to our skin and body! Honestly, a simple raw milk massage worked for me, plus just staying hydrated. Don't worry too much, let your body heal first.
I can only share what worked for me postpartum. My mother made a paste of besan and curd, and applying that regularly really helped lighten my patches. It takes time but it's safe.
Listen to me, don't rush into using any chemical creams right now, okay? Your skin is still very sensitive after delivery. Use a bit of fresh aloe vera ghar pe and let it heal naturally.
When I went to my parents' place after delivery, mummy used to make a haldi and chandan pack for me. It took some time but my skin got so much better without any heavy products.
I know it feels so bad when you look in the mirror right now, I felt the same way. But please give your body some time, it did something so beautiful. This pigmentation will fade slowly, just keep moisturizing.