I had the exact same feelings when I was pregnant with my son (1st pregnancy). It's okay to mourn your pre-baby life (I still do sometimes). You might not feel like a mom now or even after your baby is born. That's okay. The best thing to do is take it one day at a time and seek help if you need.
Yes, having a baby will completely change your world. Personally, it made me appreciate my body so much more and gave me a new perspective on life and what's important.