It sounds super counter intuitive but I recommend newbies weigh themselves multiple times a day for the first few weeks or months and write down the date and time of each new low (or use a tracking app) to get used to the idea that your weight fluctuates wildly throughout the day.

Just because you got a bad weigh-in doesnt mean the diet didnt do anything all week. A salty carb heavy meal last night (that was still within calories) can fuck up a weigh-in bigtime.