Nipples Leaking

I'm 18 weeks today and last night both of my nipples starting leaking some stuff it wasn't a ton but it was enough to go through a folded up paper towel (I wasn't expecting it so that's just what I had to put in there lol) I have read about this happening to people early on but my nipples got like super huge when it happened and they've shrunk back down.

This is my first pregnancy so I was just wondering if that's all normal?

No one ever really explains what happens when they leak so I didn't know if them getting big during that was bad or not.