I've felt the same way before, I know exactly what you're talking about. Like, you really just want to do what you're doing and be left alone, but people keep seeming to go out of their way to bother you, because they think you look bored, or need company or you're sad. Meanwhile, all you really want is your space but you don't want to sit in your room, or hide away in a hole. Why can't you just sit somewhere and be left alone? You don't want to be mean and just tell people to shut up and go away, so you have to sit there and tolerate their inane boring small talk.
I used to feel like that all the time in school or when I worked customer serve retail jobs. If you're a customer and you need something, fine, but if you just want to chat because I don't look like I'm doing anything, GO AWAY!
Sometimes at home I feel the same with my girlfriend. I'll just want to sit there, quiet, and be left alone but she'll keep asking if something is wrong. I'm perfectly happy just 'being', but if I'm not talking or doing something, she wonders what I need. Sometimes I make excuses to go out or do something up in my office, just to be alone. I love her more than life, and if she had something she wanted or needed me to do, I'd do it, but sometimes I just want to be left alone, but she thinks that means I'm upset or something is wrong.
Is there? I don't know. But you're not alone. I'm a very social well adjusted person most of the time, too. Just sometimes... I wish there were no people.