Welcome Shen; I would suggest you start tracking your mood and also note what you eat, drink, medication, stress etc. to see if that's triggering the mood swings. I found a good one online at:

http://www.medhelp.org/land/mood-tracker

There are tests on this site to take, but in saying that self diagnosis doesn't replace speaking to a mental health professional about your concerns. I hope you find this site supportive.