Mirandy, sorry to hear that you have been feeling Blah, but I know exactly how you are feeling. I have been feeling that way for a few days now.
About the pizza, I would suggest the same thing, take a smaller piece and add either fresh veggies or a salad too it and then if you still feel like cake, only take a sliver(I mean a very small sliver.)That way you won't have felt like you completely deprieved yourself of the sweets, but yet you won't have blown you eating.
Good Luck. I hope your feeling better.