I often feel like that. I think in recent times, what with the overpopulation (especially in NYC!) and the technological closeness given to us by the internet and cell phones, we're not really as alone as a lot of us need to be. It's not your fault; people make demands on you, or force you to be social when you don't want to be, or even can be. If you can swing it, go somewhere outside the city, or to a local park, turn off your cell phone and just be alone for as long as you want. One day in high school, I carried around a little card that said, "no talking for today". When people asked me something, I'd just present the card. You'd be surprised how little I needed to. I found that we often talk because we're supposed to, not because we want to. I'm not suggesting you do this exact thing, but if you found some way to pull off not talking for a day, it might help.
good luck, and much love