MM, three weeks probably a bit early - some people do it this early and no probs, but I'd say if you don't have to, don't bother just yet.
MrsB, I do think that bf is the best thing you can do for your child - but I firmly believe that for those women who wouldn't now have happy bfing experiences, society needs to change. Currently, we tell women during pregnancy that breastfeeding is It. Then they're let down massively by overstretched, under-trained staff postnatally. No bloody wonder they're resentful of the whole thing and turn to formula with lioness roars of "don't make me feel guilty"
If I could explain a bit more about why it's the best thing you can do for your child, because I know it's the sort of thing I'll be leapt upon for - "above loving them?".
If a woman is well-supported, well-informed and has people who offer her the right kind of help (practical help round the home, with older children, with bfing support), should she so need, then breastfeeding will be easier. If she's allowed by society to spend as long as she needs getting used to being a mother/mother of two or more - and by that I mean she's allowed to mooch about in her PJs, dozing, feeding and eating food other people have cooked, whilst she's revered for bringing new life into the world by those who ask after her - she'll find breastfeeding easier.
As it is, we expect too much of ourselves - because we're too worried about being judged by each other - and because we set ourselves unrealistic targets (often fuelled by celebrity unreal experiences). Look at this thread - it was started because the OP hasn't lost the weight she feels she ought to have done (however lightheartedly).
It's wrong that we view motherhood and breastfeeding as things women must do alongside everything else - and that bfing is the thing that "gives", not the other, often far less important, things - if more status was given to mothers in society, we'd live in a kinder world.