Leaky boob

Anyway I was having sex the other day and I was getting my nipples sucked and as she was doing it she makes this weird face and she's like there's something coming out. I didn't believe her so we turned a light on and she starts to squeeze real hard and you can see this almost clear sticky stuff coming out. Tasted salty and metallic, what the heck is this? Has this happened to any of you? I'm 18 I'm not pregnant obviously lol