Hi there,
I have masturbating since probably the age of 11 and I remember I used to get the most intense orgasms ever by rubbing my clitoris. I am not 17 and throughout the years the intensity of these orgasms has gone down so considerably that will I have climaxs so weak I can barely feel them. Even during sex when guys rub my clitoris I literally can't feel anything. I no this is not normal at all and really want to be able to have enjoyable orgasms again.
I'm with the last poster: you can get desensitized if you masturbate too often, and especially if you use a vibrator. If you're wondering how to climax and why you can't climax anymore, another thing that's really interesting is that your ability to orgasm varies with your menstrual cycle too. If that's not what is going on with you, your inability to climax is probably due to "too much of a good thing", though.
So, what should you do? I'd experiment with masturbating in totally different ways. If you usually use your hands, try a vibrator, the shower head on a high setting, or even a pillow. Try different positions, different times of the day, and maybe even try reading an erotic novel while you masturbate. Take it slow and focus on getting aroused, not getting to climax. It will happen again eventually.
Do you use a vibrator? If not try that and see if it helps.