You never mentioned your age but I'm guessing you might be about the same as me (I'm 20). I'm only 9 days sober and I feel like I understand some of what you're going through. Being so young I definitely question whether I'm truly ready to give it up for good. I mean it seems like for most people my age drinking/using is the major social activity. I'm in a fraternity in college so pretty much everyone parties a lot and it's hard not to feel like I'm gonna be left out.
You've probably heard this before, but taking things one day at a time has helped me a lot. It's difficult for me to thinking about not drinking/using again FOREVER but it's not quite as hard to just not drink for TODAY. I've noticed even in the short time that I've been sober that the cravings get less and less each day and I see the advantages of sobriety more and more each day. Personally I've set the goal for myself that I'm not going to drink/use at all for a month NO MATTER WHAT, and then at the end of the month I will be able to choose with a clearer head whether I want to continue in my sobriety or go back to the life I was living.