Lactating after not breastfeeding?

This is so embarrassing. But I have been having boob pain recently and because I'm on my period I didn't think to much of it. But then it started to feel like a milk duct pain kinda. So I squeezed and some white stuff came out of my nipple. I haven't breastfed since my baby was 4 months... What could this be?? Is that normal?