I'm I wrong for not being happy...

This is my third pregnancy and will be third baby. I have a 7 year old, a 6 month old and when the new baby comes I will have two children under the age of two. My 6 month old will be just turning one! 
My husband and I have been together for 8 years and our 7 year old was such a joy and being pregnant with her was a amazing! My my second I really didn't feel anything for the pregnancy until just about the end.. It took me a bit to get as close to her as I am with my first child. Now, I'm pregnant with our third and last baby (just about 16 weeks) and I don't feel emotionally attached at all. I feel awful about it but I really don't. 
I'm scared to think that it will take me forever to get attached once she/he gets here as well.. 
To be honest, this time around I just haven't felt myself. I feel hopeless and feel as if there's just so much weight on my shoulders. Is this okay to feel this way? I feel like a horrible person!