I have extreme dark underarms! How to fix this.

My neck area, my back area, my kneesz my underarms are dark. I assume it's hyperpigmentation.

It's not insulin resistance as when I use products such as masks, exfoliate, shave, or use Aha Bha added underarm roll on it goes away by 50%. But I'm not able to find something that I can use religiously.

I checked a while back, i didnt have insulin resistance back then. And I've had this issue since childhood. Please help.