Yes, mood swings are a common side effect of quitting smoking:

http://www.quitsmokingsupport.com/withdrawal1.htm

I know that doesn't help much (I remember when I was a 20-something and got depressed/suicidal before my period and knew it was from getting my period; did not help how I felt) but maybe you can look further ahead to April :-) and what you want to be doing then, and how much money you will have saved (you are putting aside the $50-$200+ a month in cigarette costs to do something exciting with, aren't you?), etc.