why am I feeling like this?

Hi everyone.. I'm coming 21 next week, have a boyfriend off 2 and half years.. and the last few months all I want is a baby and it's all I can think about. I love the whole family idea, we have are own car both work and live in my mum and dads house. 
When I say to him about it he starts to pick out names so it gives me hope then when I say again he doesn't want to talk about it. 
Help why am I feeling like this??