How come I don't enjoy beaing eaten out by my boyfriend??

First of all, I want to affirm you as a wonderful person. There is nothing wrong with you, you just aren't enjoying something like other people do. This proves you are a unique individual who is precious and awesome. Sex is about self fulfillment, so you are not just having sex, when this is going on, or you would be finding a way to enjoy it no matter what. Instead you are acknowledging that you don't enjoy it, and seeking the reason behind that.
I would like to encourage you to do two things. First, think about what is happening, when he is doing this. Is he investing in you emotionally, mentally and spiritually? If so, then this just isn't for you, right now. If not, you may be sensing that he is more interested in your body, than you. Since your body is temporary, and you are permanent, that is a spiritual distraction that makes it hard to enjoy the physical.
Since no more than 20% of a healthy long-term relationship is physical, is he investing in the rest, or simply trying to get you to do what he wants you to. Is he using this as a bargaining chip, or a way to give you pleasure, so you can feel his love for you. He should be investing in you, intimately in other ways, before he turns to the sexual.
You might like to work through the book "The Five Love Languages" and see what your languages are, and how they interact with his.

Next time instead of concentrating on what your boyfriend is doing to you, fantasize about who you would like to have sex with. For me, I just have to think about Teri Hatcher and I always get off on what my girlfriend is doing to me.

There could be a number of factors that are in play. First, sex is just as much of a physical process as it is mental. If he doesn't try to 'turn you on' before hand, the actual sex isn't going to seem 'sexy'. Try some foreplay or have him massage you everywhere before he gets down there. You have to be completely relaxed and ready when it starts. Also maybe his techniques aren't the best because it is his first time. But you know your own body better than he does, so you should feel comfortable telling him what feels good and what doesn't. I know masturbation may seem like an immature thing (especially to women) but it really is the foundation of getting to know your body and improving sex. If you know what you like, then let him know.

Women can generally have a harder time receiving pleasure from sexual interactions than their male counterparts, because there are so many more nerves located in the vagina than a man's penis, thus making it much more complex and difficult to stimulate. Some women go their entire lives without experiencing an orgasm.

I am no expert on the subject, but have learned this through various sources. I hope you can build upon this, try new things, and have fun!

-Shyyz