Extremely sore nipples, am I pregnant?

First thing you need to do is relax. It's probably period/hormone related. If you're stressed it can alter your period schedule. Also, if you're spending a lot of time in close proximity to other girls, your periods can sync up, changing your regular schedule. The seasons are changing too, people don't realize how much that has a play in how they feel, especially if they're too bombarded with modern life to notice.