I was a 12c pre preg, then up to a dd during preg. The first few days after my milk came in my bbs were HUGE and hard, but I didn't really wear a bra for weeks because I was at home (didn't leave the house for three weeks). Then I went and got fitted at the aba shop into an e cup and stayed in that until dd was feeding less at about 12 months or so.
I wouldn't rush out and get new bras in the first week, be ause your milk supply isn't really established until 3 weeks.

I am currently in a dd at 30 weeks pg and think it'll be pretty similar.