um...for my own experience, my first time have baby ,my breast are not big and not sensitive. But this time I have my second baby, my breast grows big and very sensitive.
Your rib cage will increase during the course of pregnancy to increase lung capacity and room for the uterus as it grows higher: http://www.healthguidance.org/entry/16152/1/Rib-Pain-in-the-Course-of-Pregnancy.html