Exactly, it happens to me too. I can't let myself think too much or sadness and doubt creep in. But all that is normal. Before I had my last son I had 3 miscarriages and I was such a mess, inconsolable really. I thought it would never happen and then bam, when I was literally not trying I got pregnant again, and it stuck!
So, sometimes I need to remind myself that I am walking in old familiar shoes and though the road stinks, and my feet hurt, I will eventually get to the destination I seek just like I did last time. Hugs!