My boobs got a little bit bigger during pregnancy but didn't get huge until 3 days after having my son. That's when my milk came in. and it felt like i had implants they were so hard and engorged
Your milk doesn't come in until after you give birth. Some women it takes up to a week but it usually comes in with in three days. Your breast will probably get bigger once your milk comes in. I would not be concerned. The size of them has nothing to do with the production of milk.