Starting anything new can be stressful. Starting a new job can be one of the most stressful things - especially if it's your first real job. Some people thrive in new social situations and love meeting new people. Those people should be in sales. I am sure not one of them. Your first days on a new job may seem like the first days at a new school - when you were trying hard to make new friends and hope you weren't going to end up eating lunch at the goth table.
Here are links to a couple of tips: