I lactate, but I'm not pregnant.

So. Ever since I was at least 14 years old(maybe before). Before I even started being sexually active. I have had white milky stuff come from my boobs. It literally squirts across the room. And if I don't drain myself, my boobs get itchy and sometimes even painful. I don't swell or anything. I've just always had this issue. At first I just thought it was a period symptom.. But I do it all the time. I could never understand why I did it. Dose anyone elses do this? Or dose anyone have an explination as to why it dose this?