I take multi-vitamins just cause they are good to take, not for HRT. I don't know if it affects it or not. I also eat and drink lots of soy, despite people trying to convince me that it's "bad" for HRT. I don't think it is, since the estrogen in them is pretty weak. I'm a 36B, and still growing. it just takes time, and genetics. Some people will get bigger or smaller than others.
I don't really buy into those breast enhancing herbs, since I've seen it fail so many people. They may help to some degree, but probably not as much as regular HRT. Some herbs can simulate the glands and make your breasts appear fuller (cause they are retaining water/fluids), but once you stop your breasts size will go down that little bit.
But then again, for some people it might work. As far as I know, there are no actual studies done on the effectiveness of herbals.
Being healthy, active, and eating a well-balanced meal will probably help you more so.
--natalie