Is it normal i want to feel emotion, but i can't?

I want to feel emotion--no, I'm not drained of /all/ emotion, but it seems that I lack the essentials.

I want to mean it when I say something, but it's hard to--it all sounds robotic. I can't feel happy when I smile and say "thank you" to a compliment. I can't feel mad when I yell, and I can't say nice things and mean it. At times, my chest feels heavy, and (weirdly) sad. I feel like I should cry--no, I /want/ to cry--but I just can't. The tears won't come out.

I want to scream, to feel furious and angry when provoked and things don't go my way. I want to feel light and breezy when I'm happy. But, those emotions won't come to me. Instead, I feel empty and numb.

When disappointed or when someone is angry or lectures me, I start to feel numb, and I just can't seem to care. When I see something that isn't socially correct or filled with contempt, I want to yell at them, but all I feel is a scary smugness and the urge to make that person's life miserable, except it's without hate or loathing, it's just a need.

When near others, I pretend to have emotions. I pretend to be content, to be happy, to be frustrated, to be mad, to be sad and sympathetic, when it seems required of me. But I just can't feel them. Instead I find it disgusting that people act with strings of emotions, spilling out before them, and I just pretend to react.

Is it a defense mechanism? Or am I incapable of feeling the way I want to--the way I'm expected to.