Everyone's so excited for my twins...except me.

I don't know what's wrong with me. I am pregnant with two twin boys due in march and everyone is so excited for them. I already have one daughter and my pregnancy with her was great even though it was a "surprise". I felt connected with her since day one but with these babies I don't feel that way at all. I feel like I'm a surrogate having someone else's children. I care enough about them that I would be upset if something god forbid happened, but I'm not looking forward to them being here at all. I fake smile through every sweet comment about them so I don't seem like a terrible person. What do I do? What if I still feel like this at birth? They deserve the love I feel for my daughter and I'm beyond terrified that I'm incapable of doing that.