I think that you should put your mind at ease, in the sense that this is a common urge at this point of a woman's life. I think that it's perfectly natural to want that and nothing wrong with it but by the same token, take heed of the advice here regarding protecting yourself from an "accidental" or impulse driven pregnancy. I'm sure you're already doing this but while you're vulnerable be extra vigilant about being cautious not to get pregnant.

Other than that part, for the urges, I think don't feel down about it but maybe this will help. So you're sure you're not ready. Maybe your brain and heart need to be on the same level. Try like others have mentioned, volunteering at an orphanage, take care of others' babies if you can and be around them not just to visit but actually see, feel and get in touch with the reality of what it takes to have a child of your own. I know that sometimes we idealize the dreams we have, whatever the idea is, job, career, mate, and for you, child or children. Sometimes the vision we see is all candy canes and sunny days whereas the reality is, kids take a lot of work. Mind you they are every bit as rewarding to a person that is ready for parenthood but nevertheless they are work. Sometimes our brains forget about the consequences of our dreams and we only see the good. Perhaps being around a daycare, orphanage or even babysitting very small children will help your mind to see the whole picture. Even just hanging out with new mothers, you'll see the stress that goes along with babies in spite of how much their parents love them to death. Just find ways to help yourself to see more than the wonder that is pregnancy and motherhood but also the thorny parts of it.

Hope this helps.