I can't stop being negative and wanting to die (not urgent). Help?

There's nothing wrong in particular I just find life not worth it and stressful. Also I feel pretty much alone like the people i consider friends really aren't that good friends and I just realized that. Even when I'm having fun it never lasts and I go back to feeling bad. I never go out at all because I never seem to be invited to anything, So I just end up feeling down, It's ruining my social life because now my friends are getting tired of me. I just hate being this negative downer. Any help/suggestions. Again I just don't find life worth it.