Baby Fever Vanished?

Ok so I REALLY wanted a baby.  We've been trying for over a year, and I had two miscarriages during that year.  This time I got pregnant before we were even supposed to be trying again, so we weren't actually "trying" that time we BD'd, and the pregnancy was a (happy) surprise.  Now I am almost 18 weeks pregnant and all of my excitement and desire to have a baby has turned into fear and nervousness - like what did I get myself into?  I'm 34, married, we own our own home and have good jobs, and a very strong support system from my family.  Is it normal to have these feelings?  It's not that I don't want my baby anymore, and I'm sure I'll love him when he gets here but the drastic change my life is about to take is scaring me!  Please tell me someone else has felt this way and everything was fine when baby arrived!