What Causes Bad Mood Swings Post Menstruation?

For the last few weeks I've been having pains in my stomach, constant headaches, toothaches, sore breasts and a sore back. These are sypmtoms that I'm about to start my period, but my period finished last week. Since my period all these things have gotten worse, and I've been having bad mood swings. This was also my second period for the month, and only lasted 2 or 3 days. What do you think this could mean?