SO doesn't want baby but I do!

Me and my SO has been together for 2 in a half years and he's already got a child (not by me) and he says he's not ready for another one just yet because a baby is expensive and he has a lot going on right now. I completely understand where he's coming from but I want a baby like NOW! I had a pre-term delivery almost 4 years ago, in a previous relationship, and since then I've always wanted a baby. He doesn't know when he'll want another baby. I'm almost 24 and I don't want to keep waiting on something I want so bad. During sex he has asked me if I was going to have his baby. I kinda feel like he plays with my emotions and I have cried a lot about this situation because I don't think he understands my desire to have a baby. Any suggestions on what I should do??