i got this too, v sore ribs when i sat down for long time in certain bras (this was early on)... I found a swap of bras to maternity bras helped a lot - get a good fitting donw. I havent grown much (1 cup size so far) but the chg in design helped me a lot - even now I know diff bras give me more or less pain...
Also an underwire will def hurt you more (and I think they are not recommended in preg anyway).
Good luck with your preg!