Is it normal to feel this way the day my gf got pregnant?

It's been bothering me lately, I love my girlfriend and I'm willing to give everything even my life just to see her happy. I want her to be my first and my last girl we have a descent job. and I always dream to have a family with her. then the time came when we had sex and i got her pregnant. once it was confirmed she was very happy. but why can't I feel the same thing. like I know I want to have a baby with her but I feel nothing...BLANK...like "oh there's our baby how cool" impression like that. I just do the obligations a future father will do but i don't feel that excited but still I love her and also to our baby. it's just why am I not to very excited about it. months passes. she gave birth to Denise our baby girl. but still i just don't feel like overjoyed than her... I mean of course I love my daughter but why Im not happy with it.its hard to explain... is it a mental disorder or what? does this have something to do with dual persona? i know its hard to understand my situation and you may laugh at me and think of me as wierd but It's very really hard to explain. and I am not telling this problem to my wife because I'm scare to hurt her feelings. help pls...