AIBU to feel massively pissed off, give up on the diet and have a bar of chocolate
YABU. The most important thing is that there are several factors that influence your weight that have nothing to do with how much fat you are carrying, which is what you are trying to lose.
One of the biggest pieces of bullshit advice given to dieters is to 'weigh yourself only once a week' because then you have absolutely no idea of fluctuations that can affect your weight by several pounds.
Weight on it's own tells you little about how much fat you are losing.
Go by the feel of your clothes, waist measurement and much more frequent weighing, to get a handle on the fluctuations. Try twice a day and you'll see how much your weight goes up and down. The app mentioned by olli above looks good for this.
But make sure you take the fluctuations rationally. Drink a pint of water and you will weigh more, but you haven't got any fatter.
You may retain water and weigh more before your period, but you haven't got any fatter.
You are really dehydrated and weigh less because you had a load of alcohol and little food for dinner last night, but you haven't got any thinnner.
You appear to have gained 3 pounds because you ate pizza yesterday, but that's because the fatty, carby salty deliciousness has topped up your glycogen stores to bursting but you haven't got any fatter, not because 'you only have to look at pizza to gain 3 pounds' that sort of thing.
Stick with it and good luck. You're doing the right sort of thing, so it will work, but you can probably make it easier for yourself and be less hungry by doing something like Slimming World, where you can eat unlimited amounts of basic low fat healthy food like fruit and veg, pulses, eggs and lean meat and fish without any weighing or tedious app logging.
Just make all your meals frm this sort of food and the only things you have to limit is dairy and bread to a small portion of each every day, plus no more than 300 calories worth of obvious crap like cake, biscuits, crisps, alcohol etc.