breast milk? And not pregnant

Ok so I just started ttc this month. I’m taking prenatales just because I’ve heard it’s good to start taking them early. Well my breast were sore and heavy like 2 weeks before my AF so I thought maybe I could be pregnant well no on the 27 my AF came I’m done bleeding but I still felt my breast heavy well I started to feel them to see if there sore (and they are a little) and milk came out 😱 my youngest is 3 yrs old never breast feed her. And never had milk come out if I’m not pregnant. What’s going on? Is it cause of the prenatales? Help. 😩