Why does my weight keep fluctuating?

This is common, especially when one is trying to lose weight. There are a lot of factors that contribute to this: Water weight, salt intake, gas, not going to the bathroom, caloric intake and whether food was lean or fat, and how much you exercised or not in the days before. Even the time of day that you are weighing yourself makes a difference. You are typically lighter in the morning before eating or drinking than later in the day. If you are gaining muscle from working out, the scale will read higher as well. Muscle weighs more than fat. The best way to keep tabs is by using a tape measure to measure your waist or other body parts to see if you're losing inches. Weigh yourself only once a week, same time of day/best upon waking up, in the same clothing each time you weigh yourself.

Because your body weight fluctuates about 5 lbs throughout the day because of eating, drinking, peeing, sweating, pooping, etc.

Stop f*cking weighing yourself everyday. Weight loss doesn't happen overnight. Weighing yourself every single day doesn't help your weight loss.

A person's weight can change 5 - 10 pounds each day depending on what you've been eating and doing. Usually just 1 - 3 but can be more. Nothing worry about.

Because you eat food, breathe in and out and go to the toilet. The morning after several beers and a curry, I can see my weight fluctuate by about 7 pounds in about 5 minutes.