Disclaimer! I am not anything close to an expert! These are just my thoughts.
If your diet is drastically different than what it was, your entire body chemistry is changing. I doubt it is one food. It's more the combination of foods that you are no longer eating. Hopefully, as your body becomes more accustomed to this new eating style, your moods will even out, also. Give it some time. Try to keep busy. I wish I had better advice, but maybe someone else will come along to help out, too. Good luck! Don't give up.
Annie
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard