It might be that you're getting over stimulated. The clitoris is a very sensitive organ, and while some girls can take a lot of attention, other girls just can't handle it. I've noticed that girls also misunderstand their own body, thinking that the discomfort is something bad, when it's actually arousal or something like that. I suggest exploring yourself to find out for sure. You can't hurt yourself, unless you're too rough or try to go too fast.

It definitely sounds like you're just really sensitive. Try lube, your fingers, shower heads, vibrators, whatever, but go slow and don't try to force yourself to orgasm! Sometimes masturbating through clothing can keep you from over stimulating yourself. If you feel your body start to tighten up, and it feels unbearable, you're probably just about to orgasm. I don't know of any diseases that cases pain during a female orgasm, especially at your age. The hymen isn't directly connected to the clitoris either, so that shouldn't be a problem. However I'm not a doctor by any means, I just understand my body. Good luck, and just remember not to force anything! It's your body, you should enjoy it!