Its not too early for a maternity bra! My boobs seem to grow very very quickly (I am now and E cup and not stoked about it!) and I think they are growing again. I hate maternity bras - I think mine are awful to look at and not very comfortable (yes had it professional fitted I just want my underwire back please) but you should be able to find some funkier ones in a C or D cup.

I am with Sarah - I am returning to the underwire as soon as I stop BF'ing so I figure the mat bras are a useful investment!