I have come back to this post, because quite frankly, it disturbs me.
Here, we have a young woman, mother of 1, with another baby on the way. She is worried and feeling stressed about having another baby and the responses she gets here are to slam her for her past decisions.
Perhaps she posed her question poorly - perhaps she could have asked for help, rather than asking God's will for her situation.
I agree that sex before marriage is far from ideal, but what is done, is done. God knows that, and God can turn things around.
I believe that God's will for your situation Chava, is that you become the best mother you can possibly be, and that you raise children who love and serve Him.
Given that I also think sex is designed for marriage, and given that you are engaged to the father of your children, I would suggest that you go ahead and formalise that commitment and get married - sign a piece of paper ASAP and make your fiance your husband (even if you can't afford the wedding of your dreams just now).
I won't get into the pros and cons of quiverful. I don't think that is something you really need to consider RIGHT NOW - if you are already pregnant, what matters now is your children, your relationship with your children's father, and your relationship with God. Get those things sorted, then worry about the rest.
I know that is a little vague, but I just wanted to offer a "shoulder" for support if you feel that you need one. I am willing to listen, even if I don't have all the answers.