Breast milk and not pregnent?

Ever since I received my period when I was 13 years old I have always had this milk like discharge from my breast and when I read online they said some women can produce milk before pregnancy but I couldn't really find the answer I was looking for. Can anyone help me figure out what it is or know of anyone else who has this problem? I have never conceived a child before I don't know how its possible to have discharge that's like breast milk though.