OMG the itchy!! YES!! I have been getting this (unfortunately at work I don't have my own office with a door I can close, I'm on reception and I'm always itchiest when I can't scratch!). I haven't gone to a maternity bra yet, still wearing my underwire because it's not uncomfortable yet, but yeah, I just assumed it was the fabric of the bra or something? But growing makes sense I guess.
Glad I'm not the only one!