afraid of sex

I'm afraid to have sex. I don't know why, I have never had it, I'm not fat, I don't think I'm ugly, so howcome all of my friends talk about it like it's nothing and I'm just afraid to do it. I know it's natural, I'm not worried about getting pregnant, I have no clue what it is. There's been a few guys I've been head over heels for and just couldn't bring myself to do it. Everyone's like you'll know when your ready but this doesn't feel like me being too young, this feels like a fear. And I really don't want it to be like this, I want to enjoy my life and the people I fall for.