I need Sex now......

I'm a college-going girl aged about 22 years. I hear all the while how important the chastity is. Earlier, I too, thought likewise and hated even the idea of having sex before marriage. But no longer. Looks like my two years younger sister also have started feeling likewise.
My craving for sex is growing up by the day and looks like I would go crazy if something is not done soon. Many boys are visibly interested in me too. But I don't seem to have courage to travel the list mile.
One of my friends advised me to masturbate. (Oh! how naive to think I wasn't doing that already?) The other night, I accidentally put my hand over my younger sister' boob and then squeezed it. She seemed to enjoy it. We have a common bed. Wonder if I should further the matter as we both need sex. And that too, NOW!