6 weeks postpartum i have brown spots all over my breasts and darkn brown on belly button what is this and when will it go away i'm caucasian btw

Hyperpigmentation: Many women will experience darkening of the skin, usually around the nipples, abdomen, forehead, upper lip and cheeks. It is from the increased hormones with pregnancy; some women will even develop these symptoms from birth control pills. It usually goes away eventually. Use sunscreen in the meantime to avoid further darkening.