I don't know why this is an the aas forum, this is psych stuff but I'll leave it. A lot of really good comments from everyone here (except for the one who said to go talk to other girls). This has nothing to do with aas...it's a problem in your relationship. First thing:
1. STOP NAGGING HER FOR SEX! Does it turn you on when someone is constantly bitching, complaining, and whining to you? Fuck no...makes you want to get away from them. I think talking about these issues should be limited. The problem isn't talking, the problem is sex. Figure out the things that she likes without talking and start doing them.
2. STOP FOCUSING ON YOURSELF. Most guys (hate to say it, but inexperienced guys) are extremely selfish with sex because their drive is so high. Slow your ass down and think only about her. When you do BRIEFLY talk about it with her, don't bring yourself up at all. Talk about what she wants, not you. If you are patient and figure her out and don't focus on yourself, you only reap the rewards.
3. REINFORCE THE HELL OUT OF ANYTHING SEXUAL THAT SHE DOES. When she does anything sexual, let her know how awesome it was (even if it wasn't), how much better you feel, how much closer you feel to her, etc. When a woman is confident in the bedroom, she tends to want to do it more. Like if someone is confident in their appearance, they tend to look in the mirror more.
4. STOP JUST HAVING INTERCOURSE. A lot of people limit their sex life to intercourse...which for most women isn't the most exciting thing in the world because they might not get optimal stimulation through sex...this is normal. Also sex is time and energy consuming. Sometimes you just don't feel up to the task. Go down on her spontaneously. Don't try to have sex, just get her off and go on with your day. This also helps take the focus off of you whining for sex all the time and let's her know that you like to make her happy too.
5. STOP BEING AVAILABLE ALL THE TIME. Give her a chase. It's funny, but we tend to want things more when we can't always have them. Most women know they can have sex whenever they want, which makes it boring. Not always being up for it or acting like you want it can be very attractive, trust me on this one.
6. START TOUCHING HER MORE IN SEXUAL WAYS WITHOUT HAVING SEX. When she's brushing her teeth or cooking, come up from behind her, put your hands on her waist and kiss her neck and back, then walk off. If you're watching a movie or having dinner, rub her leg and get pretty north and then just back off. Don't say anything about sex. This kind of touching gets it in her mind and then you not nagging or bringing up sex makes it much more appealing.
Stop bitching to her and turning her off. Try these things...they work, every time.