Maybe you are experiencing depression..drastic mood swings can also be a sign of bipolar disorder.
Why Am I So Moody?
Depends on old you are, you might be going through the menopause, but we all get like that some days, and its some times nothing to do with the changes in life, but our lifestyle and our diet.See your doctor and speak to them about the issues. People will always suggest different symptoms, but without talking to your doctor you won't be sure.
If your young like me then it could be because of puberty or because your going through your monthly hormones, but even when its not my 'time of the month' I am still moody because of my HORRIBLE sleeping habits.