According to this article, my problem may simply be that I am an introvert trying to live my life as if I were an extrovert and failing miserably:

Extroverts are energized by people, and wilt or fade when alone. They often seem bored by themselves, in both senses of the expression. Leave an extrovert alone for two minutes and he will reach for his cell phone. In contrast, after an hour or two of being socially "on," we introverts need to turn off and recharge. My own formula is roughly two hours alone for every hour of socializing. This isn't antisocial. It isn't a sign of depression. It does not call for medication. For introverts, to be alone with our thoughts is as restorative as sleeping, as nourishing as eating. Our motto: "I'm okay, you're okay—in small doses."

Two hours alone for every hour of socializing? Now that I'm working in this tiny office around my officemate all day, I'm lucky if I get an hour to myself each day. At least I feel like that's the case. I don't know how much time I actually get to spend on my own, between work and friends and family, but it doesn't feel like enough.

Or it's entirely possible that the article is all bunk.