I'd bet that you gained because you did not eat enough. A stressed body is one that is not getting what it needs to function. A stressed body holds onto fat and water. Not eating lunch is stressful.
A good rule of thumb for calories is 10x your current body weight a day. This number helps to satisfy your basal metabolic functioning - this is what your body needs to do everything it has to do if you were to stay in bed all day. It does not take into account any activities or your lifestyle.
Having a history of yo-yo dieting and/or starvation dieting will mean that fat loss is going to be slower and possibly more difficult. You have a metabolism that needs to heal and it needs to be fed.
Chances are you've been very low on protein for a while - your body has some work to do. Hormones, muscles, cell repair are all the function of the protein you eat. While this may end up reflecting an increase on the scale it is a) temporary and b) probably muscle. Muscle takes up less place than fat - so while a pound of each is still a pound scale wise you actually end up re-composing your body. You weigh the same but you are smaller.
Have you taken measurements? They are a much more accurate indication of fat loss than a scale will ever be for the reasons mentioned above. I spent a 6 week period where I actually gained 2 lbs but lost over 3 inches on both my waist and hips - If I had gone with the scale I would have thought I was gaining weight, instead of losing a dress size.
Also, you might find that CAD is not the program for you. Many people cannot handle the reward meal - it sets off too many carb cravings. I'd keep a close eye on how I felt after that meal and the next morning to see how it was effecting me.
Lastly - it is not possible to gain 2 lbs of fat overnight. Unless of course you ate 7000 calories over and above what you need to function. Highly unlikely
What you're seeing is water bloat - possibly from the carby reward meal, and possibly from retention due to eating too little.
LCing is about repairing insulin resistance and learning to eat healthy and nutritious whole foods. Try to keep your calories up and work on getting past that "less is better" mindset that low fat/ restricted calories ingrains in us all. I notice you went through the Success Stories forum - it may do you some good to keep revisting that place. Those people did it, and they did it by eating, not by starving themselves.
Best of luck,
Nat