Of course, attempting to pressure your partner into having a baby when he is not ready yet is a bad idea all around. But if you feel this burning, sometimes almost all-encompassing wish to have a baby, your relationship might suffer if you just stop talking about it after your partner says, "not yet". So talk about your relationship, why you love each other, and about your baby wish. Don't pressurize, but don't keep in those important feelings, either. Why doesn't your partner feel ready to have a baby? Is it that he (and here, I talk about men exclusively, because that is the most common scenario) never wants children? Is it because he feels strongly about improving your financial situation first, or get a better house? Does he just not "feel" it yet, but might later? Understanding his reasons might make things easier for you, and it also makes him feel validated. His opinion matters just as much, after all.
If your partner does want kids, but just not yet, making concrete plans for the future may help. When do you both feel you can start trying to get pregnant? Can you plan ahead, and perhaps even set an exact date to ditch the birth control? Planning ahead makes both of you feel better the partner who wants a baby knows it will happen in the future, and the one who doesn't knows his feelings are respected.
Talk to like-minded women
There are plenty of online discussion boards where women talking about their wish to get pregnant, and how they cope with their partner not wanting to yet. We can recommend our own forums, but any place where women discuss these issues gives you the opportunity to vent, grieve, and have hope.