I don't think it is cold weather since I live in a desert and its warm all the time and no I've never had a mammogram, I'm soon to be 18
I don't know if this helps but I also have small white marks around the middle of my breast, I believe they are stretch marks, but could it be that which is making me itch? Maybe there's something wrong?
You don't say how old you are? Have you ever had a mammogram?
Could it be your skin reacting to the colder weather drying out?