You do not necessarily swell up hugely when you breast feed. I was a scant B cup, and increased to a C cup while I was breastfeeding. Nine months with one child, 2 years with the other. When I stopped I went back to the scant B cup. Bohoho :-(
this may be too much detail for the guys, but when the milk first comes in, i swelled up so much that even my husband was grossed out. haha