Finding the Off Switch

Ever since I can remember I've had a problem with thinking. I am always thinking. My brain never turns off. This was wonderful when I was in school, I could always be working on papers in my head. It's not so much fun now that I'm done with school. The constant thinking and over analyzing things. I just wish I could turn it off. Nothing seems to work. I've tried journaling before going to bed, but that doesn't work. I think it's a lost cause.