Leaking breast??

Hi,

I'm 31 weeks pregnant with my first baby. New to all this so I have no idea what to expect! So would appreciate some help please ladies.

I've just woken up half way through the night to find one of my breasts wet. There's no sign of milk - I would assume there wouldn't be at this stage right? It's just wet and whatever it is that has leaked out has gone through my nightie. What's going on?