I had the flu a few days ago (chills, fever, congestion, cough, sore throat, nausea, only sleeping and being awake a few hours at a time etc), and so I had no appetite whatsoever; I managed two sandwiches, and a bag of crisps in the three days when it was at it's worst, then it was Christmas and I managed a child sized portion of dinner and a cracker later on, the next day was better and I ate almost as much as usual but yesterday and today I've been fluctuating between feeling nauseous and absolutely ravenous, I'm craving things like toast, cheese, crisps and meat even after I've eaten and I'm full.
Should I be eating more or something? I know I'm still recovering from the flu because I still have a cough, congestion and a sore throat so there might be certain foods I need to eat or some vitamin my body needs or something.
It's just annoying waking up in the middle of the night desperate for cheese and turkey on toast.
(Also, I'm not pregnant; just in case that was what someone was going to suggest).

A sedentary adult woman needs about 2,000 Calories per day, so think about it to prevent overeating.

It's possible you've become dehydrated because of sweating and not drinking because of nausea. Thirst and hunger can be easily confused.