Adjusting to pregnancy and the thought of being a mom

At one point in my life I was so excited about the thought of being married and starting a family. Well let's just say that didn't work out as planned. I finished college got married but my husband at the time cheated repeatedly and we ended up getting divorced. We never had children. After leaving that situation I found myself. I was happy and my life was on track. Then I meet my now husband who is amazing. Very loving, a provider, attentive, hardworking, everything I said I ever wanted. He built us a home. We got married and now are expecting our first child. I've had such a hard time adjusting to being pregnant, sick ALL of the time and dealing with the thought that my life will never be the same. Don't get me wrong I am grateful that we are able to have children and have been so blessed. I just wonder why I'm not more excited?? Why do I always think of the negatives of becoming a mom?? I don't know what's wrong with me...