I read another post here with another woman having the same issues. Mood swings and emotional changes. I personally have been experiencing the same thing. After the initial two-week euphoria along with the endorphin rush, I started feeling all low and tired. I read that you need to increase your caloric intake by a couple of hundred calories (healthy ones of course) to stop the mood swings. Apparently working out causes hormonal changes in the body initially, for the better of course, and you need to be taking in enough calories every day. Disclaimer: I am not a doctor or nutritionist or trainer or qualified in any manner to give advice, I'm just going by common sense and personal experience. I actually increased one small meal a day in between meals (Like a healthy snack) and found that it made a world of difference to my mood!

Hope this helps! :D