I feel the same ways sometimes, even in a crowd. I can also very much understand how you feel when you have no friends to do anything with.
I recommend if anything just get out of the house and doing something. Even if it is going to the grocery store to buy a couple of things, sitting in a coffee shop, or going to the library. Strangely enough, you will feel better just being around other people.
Over the long term, another thing that helps is to join a church, organization or activity that you have an interest in. When I was in high school, I was the manager of the basketball and soccer teams, on the newspaper and the student council. Later in life I became very active in the county Democratic Party, the local Unitarian Universalist church, and other volunteer activities. An opportunity that presents itself is that my commuity had devestating flood last year; if I am feeling a little down in the dumps, I usually do volunteer work in the flood zone. I does make you feel a little better knowing that you are helping someone with a worse disposition than yourself.
As for crowds, if I am in one that I don't know anyone, I usually only stay for a short time, have something to eat or drink, and leave. Every once in awhile someone does come up and ask about what you are doing there. It can start a small (of awkward) conversation.