Why do I gain it back so easily???

Are you weighing your food? Your diary indicates general measurements and not weighing. Thee is usually enough of a caloric difference between the two to lessen a calorie deficit.

Where are you getting the exercise burns from? Your burns seem a bit overstated, which results from using MFP, internet, and machine calorie burns. Cut those in half.

You don't gain overnight just from eating a few sweets. You gain weight by eating enough over your TDEE frequent enough to kill your calorie deficit. This can happen by a combination of underestimating calories in and overestimating calories burned.

Even with the above, you could just be experiencing natural weight fluctuations, or water. .

Food with high processed carbs and sugar tend to lead your body to retain water. So if you don't normally eat those things (which from what you said it seems you don't) and you have a slice a cake and a few cookies chances are any weight you see on the scale the next day is more than likely water.

You won't gain 1,2,3 or whatever amount of pounds from having a slice of cake once every other week or what not, it actually might be helpful for you in the long run not only mentally, but also physically due to hormones and other things that I will not get into.

Just go back to your normal routine and those 2-3 pounds should be gone by the end of the week guaranteed. Of course, if that slice of cake was the size of Shaq's shoe and the cookies were extra large, then you could have gained a tad bit.

It's completely normal for your weight too fluctuate like that ave it's not a real gain. Think about this-did you eat 10000 calories over maintenance? I highly doubt it. You were eating lower carb and indulged in food that was higher carb and probably higher in sodium than you are used to. You are retaining water. I weigh daily and regularly gain or lose 1, or 2 or even 3 lbs daily depending on my hydration, my food intake and even how much sleep I had. Earlier this week I had pizza and boneless wings but stayed in my calorie goal. My weight jumped up 2.5 lbs overnight, dropped down.5 lb the next day, then stayed there for 3 days, but today it dropped another 3 lbs.

Just keep doing what you are doing and you will see a downward trend even if the scale doesn't always do what you want it to do.

I do feel your pain.

I hate weekends, because over weekends my family tends to go out alot, or I tend to take a vacation to a nearby city and hang out with friends, so I generally gain 1-2kg over a weekend, and I spend the whole week trying to lose it, and the whole cycle repeats itself again after friday. So it is getting frustrating!