It's very likely withdrawal, especially if you ate a lot of sugar and sweets. I find that when I'm feeling moody if I up the amount of protein I'm eating, as well as keep my liquids high, it helps.
Also, it's just important to recognize it for what it is--you've made drastic changes in your eating habits, and your body is fighting some of the changes, affecting your blood sugar, energy level and emotions. Try to see it that way and you will be kind to yourself and be able to ignore some of the symptoms rather than letting them take over.
It will pass as you get used to a new lifetyle of eating, and as you see results.