it is very common :) im 22w 3rd bubba and never experienced it until this time at 19w.. dont be concerned at all unless you find lumps in your breasts. devolping so much so early usually is a sign saying you wont have any probs with not having enough milk :)
Every pregnancy are different I leak in my first pregnancy at 26 weeks & now too im 36 weeks. my doc said its normal..it's the colostrum hope this helps :)