A very common observation, and trap, I have seen many people trying to control their weight be unduly affected by daily changes in their weight. I've been there myself. Step on the scale one day, weight a certain amount. The next day, weight 2 pounds less, or perhaps three pounds more. Then become joyful, or frustrated. Especially when the weight has gone up. Its easy to become real upset, discouraged, and even to the point quitting. Yeah, I have done that too. But when thought about rationally, there is no reason to be concerned. To gain two pounds of fat in a single day, you must consume 7000 calories more than they burnt off - in one day. Now do you really think that you did that, in a single day? Probably not, not if you have been trying to lose weight.
Daily fluctuations are part of the game. It is not unusual for a person's weight to change a couple pounds a day. The overwhelming cause is fluid changes, e.g., water. Drink a lot of water, you will increase weight. Sweat and urinate without drinking a lot of water, your weight will go down. For that reason, it is better to weigh yourself every week. Doing this will show the trend, hopefully a downward trend. Another tip, try and weigh yourself under identical conditons to minimize variations. I always weigh myself on Monday morning, after my morning workout, after I used the restroom. Weighing weekly while trying to do so under consistent conditions, I have an idea if what I am doing is still getting the results I want. It also keeps my focused on the long-term big picture.