At 3 months, you'll start noticing many changes to your body, including your breasts and ribs starting to pronounce themselves Your 34B may feel a bit tight. You're moving from a 34 to 36 and becoming a C cup.
At 6 months pregnant, you're not only glowing but your belly is more pronounced, and your breasts and rib cage both feel bigger. You're now a 36C.
At 9 months pregnant you're radiant, and almost ready to deliver. Your breasts may begin to feel a bit puffy and tender the last few weeks, and your ribs may feel very pushed out. You are closer to a 36D now, but not for long!
It's now 3 to 4 days after you've given birth. You've been breastfeeding since birth, but today your breasts are significantly bigger and heavier. You've increased at least a full size in the cup (to a E(DD) or more) but feel relief in your rib cage now that the baby is born. You're also wearing a nursing bra to bed for greater comfort.
You and baby are happily working on your breastfeeding relationship. Around 10 to 12 weeks after birth your breasts have relaxed in size and weight and you could easily wear a 34D.