baby fever

I'm 27 and I've been with my boyfriend for 6 months. He has a child from a previous relationship and isn't sure he wants more. I'm trying to be cool, but I desperately want a baby. I love being with him and most of the time I'm very happy with our relationship, but my baby fever is like this thing I can't shove away. It doesn't help that I adore kids and am a nanny to four amazing children. The youngest just turned one and he is just the cutest. My boyfriend and I were having sex and I just started thinking about babies and I got really sad. Is that normal?