I wear nursing pads and they never have milk on them at the end of the day, when I go without them like when I wear a nursing tank top or bra I still don't leak, I only start leaking once I take my bra off, does anybody else have this ?

Also I've been reading that this painful feeling I get in my boob's is "let down" ?, feels like my milk is coming into my breasts, it's painful,and I usually start leaking right after the feeling fades, I usually only get that feeling when I'm not wearing a bra but I have had it a few times when I'm am wearing a bra or nursing tank top.

Is that normal? What exactly is let down?