Maybe she needs a little space. I know personally when I realize my man isn't paying me as much attention, I start to feel a little more needy. Maybe she feels that sex is all that is important to you right now, and is just a little annoyed by it. Maybe you hsould try to distance yourself a little but not in the sense that she will feel that you are not into her anymore. I mean things like, don't mention sex for a few weeks. Ask a couple of your friends to go out a little more often to grab a beer or coffee. I'm really not saying neglect her, but give yourself a healthy distance. Its worth a try, she might notice.. Hey whats up with him.. and do a little something to show that you that she appreciates you. If you show her that there ARE more important things in your life then just sex, she might loosen up a little.
Also, what specific things did she do when you first got together that made you think she was a firecracker? If you had it your way, what exactly could she do to get back to that stage with you?