Check out the cannabis info here at this site (plants and drugs/cannabis) and you'll see some of the effects they list. For some people, mood changes are can definitely happen as the effects of cannabis wear off. And lack of appetite is a common result, too, as it wears off.
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You might consider other causes, too. Like are you depressed? Under stress? Going through other circumstances or changes that are affecting your mood? This end-of-the-year time can be a rough period for people who are in school. Often when young men are depressed, it comes out instead as anger or irritability instead of depression alone, and lack of appetite goes with depression, too. Could you also by any chance be developing mood swings anyway? That's a very common problem for weed smokers and non-weed-smokers alike. Just make sure you don't attribute it all to your smoking habits alone.

See what you think might be causing the problem. Make sure you're getting enough rest and make yourself eat well. Get some exercise. And if all else fails, take a smoke break and see if your mood doesn't even out within a couple of weeks. If it does, you'll likely have your answer!