Boob Question maybe TMI no picture

Has anyone experience lactation while not pregnant or nursing and on period??  Maybe because of prenatals??
​We are TTC #2 for two months now. I'm on cd4 and taking prenatals. I haven't breastfed in over two years. But yesterday my boob felt like it was leaking then later that night I felt it again and there was milk.  And when I squeezed milk came out and still is today.  I've taken two pregnancy test just to check and both negative. Anyone know what this could be or if it's normal?