I feel that way at work. I compare myself to a cat. If I want to be around people I'll approach them. If I don't then I'll avoid them. I rarely like to talk to anyone about my personal life and I chalk that up to the fact there are nosy people there that have asked me questions or tried bringing me into conversations that are way too inappropriately personal. Or this one lady like to just go up to you and offer a card to the hair salon she goes to and tells you what you can do differently. Basically saying your hair sucks, or she will talk about your weight. How ruuuude.
Other times I find people have zero interest in my interests or what I have to say. What's the point in trying.