How can I get over my guilt of having ?

Hello I am 17 and I am FREAKING OUT. It all happened about four or five days ago. For a long time I've been planning to only have after marriage or at least in my mid-to-late-twenties. But about five days ago, my girlfriend pressured me into it and--Oh I feel horrible! I have been racked with guilt. I get all fidgety and twitchy near adults, thinking that they're going to find out and get me in trouble. I can't sleep at night, and I toss and turn, when I finally do get some sleep one or the other happens: I sleepwalk or I have recurring nightmares about getting her pregnant and not going to Yale and becoming poor. Normally I was very attracted to my girlfriend and found her pretty and sweet and well perfect. But lately I see her as some sort of slut and feel like breaking up, I lie to everyone that I'm still a virgin to keep my reputation up. But still, inside, I'm like dying, I even thought of (But not anymore, so don't worry) of suiciding because now my life is pointless and when i have with my wife it'll be meaningless because I already had it, and even worse, as a teenager!!!! Im way too young IDK what I was thinking! What should I do?!?!?!