I would go to Myer or another store and get properly fitted. They will know exactly what size you will need. It is important that the breast is well supported.

I got fitted into a 12D at 14wks (was a 10B pre-pregnancy). I just recently went to Myer again because I needed to get a couple more bras, and I also thought I'd need a bigger size for when the milk comes in, and I was right. I got fitted into a 12DD.

Hope this helps!