Might want to buy some breast pads (in the bottle section of any grocery store.
I'm 20 weeks tomorrow and it started happening to me at around 17 weeks. My midwife said it's a really good sign that my breast are getting ready for feeding :)
Mine started around that time also
This happened with my first around 17 weeks. I keep feeling a tingling sensation in my breasts now and expect to find that it's started but so far nothing (20 weeks)
That hasn't happened to me yet but I got these books from a doctor's office and read that it was perfectly normal for some women to start leading as early as 15 weeks