First off, well done for making through the first five days - that's a big achievement! Just stick it out another couple of days and then you'll have a nice big loss to motivate you.
A thought on why you're feeling hungry today: are you still in ketosis? You're not really supposed to have diet coke (or any other fizzy pop) because the citric acid can knock you out of ketosis, particularly if you're not well established...have you got any ketostix to check?