i posted a similar response about i year ago i guess, when i started the WOD. i was experiencing exacty what you are, and since i just started hitting the gym after about a 2 month "vacation" due to school and work i am felling it again.
my brother has started crossfit as well, and he actually commented on feeling the same way while we were walking to the gym yesterday.
when you actually think about it, it makes sense. you are subjecting you body to tremedous amounts of stress during the WOD; probably something you have never come close to doing - at least on a daily basis! your body needs to repair and recover, and your metabolism will go up as well, all requiring you to take in more fuel.
what i did was keep my protein intake the same (a gram per lb. of bodyweight), and just started eating nuts like you are doing between meals and when you get that feeling.
hope this helps! have fun!