The growth and other changes in your breasts are necessary to help baby feed after birth, but man can it cause major discomfort. Increased blood flow to your chest (caused by surging hormones, what else?) is probably making your boobs swollen and sensitive to the touch. The soreness should fade after your first trimester, though your cup size will continue to increase as milk ducts and milk-producing cells form.
Your best defense? A supportive bra. Take a professional bra consultant up on their offer and get an expert fitting. Make sure to leave some room for growing!