Just wanted to add, it is very possible that soy milk will affect your breastmilk production, because soy has so many phytoestrogens (same reason menopausal women LIKE it, may be why younger women should stay away from it). I just did a lot of research on soy-based infant formulas and the connection to early menstruation & breast cancer in the girls who were fed it, because of all the hormones.
My own daughter received both breast milk and formula, and she is soy-intolerant now, even though she never had soy milk or formula as a baby. It gives her gas & diarrhea now so it's just dairy or rice milk. I actually like vanilla flavored rice milk!

It's pretty expensive though. Also this stuff called Almond Milks is really good too... ok I'm making myself hungry again.