veins in boobs at 14

Ok first, I know this isn't exactly strictly about the period, but it's on that topic. And I'm not prego, I'm 14. I have veins that show up in my boobs. They're visible a lot more and way darker, and more veins appear during my period. I haven't really noticed them till this year, but I never did really pay that much attention when I was taking my bra off so...