Mine came in after delivery. Not painful for it to come out, painful for it to stay in, if you have gone too long between nursings. Leaking doesn't feel like anything, except that you usually only leak when the breasts are a bit full and that feels a bit tender. When your breasts get too full, they feel a lot of pressure. When the baby starts to nurse, it all eases.
I'm 24 weeks and mine has started to leak.
No its not painful.. and not everyone leaks. Some moms dont get their milk till after delivery