Dude I feel like a freak now, I had it for a couple weeks now! I think about 16 weeks it started for me. Its NOT a sign of impending labor so your fine there. Its just your boobs getting ready. I just figured mine the need to get ready early since they get so much "attention" that the stimulation of them causes it to happen.
(that was my subtle way of say DH is a boob man :LOL