I am craving pregnancy so badly...What's wrong with me?

I'm 19 and a nursing major and my boyfriend is 21 and has 3 majors: Accounting, Finance, and Entrepreneurship.

We have a very healthy relationship and an avid sex life. I am on the pill and we use condoms sometimes. I have been wanting to get pregnant and have a baby lately and it is not like me. In theory I want to get pregnant, but in reality I don't want to since we are both in college and children are expensive. It's kind of difficult to explain. It's not even just around ovulation, it is every waking moment.

Why am I feeling this way. . .??

What's wrong with me?