Baby on My Mind

So, my SO and I have been together for almost 3 years. We live together, we talk about the future a lot etc. We aren't married or even officially engaged. The problem is that I want to have a baby. I'm so ready and I long for one, but he isn't ready. We have had pregnancy "scares" in the past and he always freaks out. I know I'm being Selfish here, but I don't know what to do. Just because he isn't ready doesn't stop me from wanting a baby. I really want to be a mommy.