The urge is built in, welcome to being female, sounds like you have lots of nice strong hormones But we are not just our hormones, other animals have the same urge but they don't get a choice, they just get pregnant wily nily when Nature decides it is a good idea (where there's enough food, water, etc.).

Sounds like you know what needs to be done before having a baby would be a good idea; I would work on the boyfriend (if he's the one you want to marry, if not, I would look for one you would like to marry) and have quite a few discussions with him about the future and what the two of you want in detail. Do you only want one child? Chances are you will perhaps be pregnant around 30 if you want multiple children, but you probably will not feel about 30 the way you do now.