All woman are different when it comes to producing breast milk during their pregnancy but for my sister she started producing breast milk a couple months before her baby was born.
For me I started producing milk from my breasts a month before my baby was born and some woman have said that they produced milk 4 months before the baby was born.
It's all normal and like I said everyone is different when it comes to pregnancy and producing the breast milk.
If your nipples are leaking, the substance is usually colostrum which is milk your breasts make in preparation for feeding your baby.
Leaking from your breasts is normal as well and nothing to worry about.