Trying to stop yo yo deiting

not easy to answer without more context.
Diet, exercise, gym etc?

There's quite a few reasons people can't control their eating like stress, proper planning, overcoming negative emotional states, poor sleep, convenience for example. As far as food is concerned one theory is it's mostly hormonal and people continue to eat the foods that are designed to circumvent those hormones which also happen to be made mostly of a food mass that is then formulated into different shapes, sizes and macronutrient combinations that are then specifically designed to be overconsumed. Examples might be cornflakes, twinkies, white bread, candy bars, artificial cheese crackers, pringles, energy and soft drinks, shakes, most desserts etc. These types of food represent over 70% of the calories consumed for the average American and there's seems to be a correlation to being overweight and obese where about 70% of Americans are overweight and obese. I think if it was easy to forgo these foods and replace them with whole foods that number would come down and it appears from statistics that people that eat mostly a whole food diet tend to weight less and are more easily able to maintain their weight regardless of the other stressors in life.

A lot of people find themselves hungry when dieting quite a bit of the time. Some people can moderate these foods without a problem, personally I'm not one of them and I consume a low carb diet/ketogenic diet which is mostly a whole food diet and one with mostly animal protein and eat until satiated and now I have to be mindful that I get enough to eat. I need around 3000+ calories to maintain my lifestyle and there are days where I'm not eating enough and lose a few lbs simply because I'm not hungry and I gauge that mostly by how my cloths fit, which is a quick reminder that I need to eat more and energy during this time doesn't actually go down and certainly feels like it goes up, strange but true and I don't count calories and have maintained this for a dozen years. Everyone is different, but that's what works for me.

most people i know who diet hit a certain goal weight, then they start to eat the way they always used to and put the weight back on. if you eat what you used to eat, you'll weigh what you used to weight.

the thing is to create new eating habits that are sustainable. it may mean you have to change amounts, foods or recipes, eating frequency, and may have to learn to budget calories if you want to splurge. i found it helped to change from full fat ice cream, yogurt and milk to the light or non-fat versions and to find snacks i really like that are lower in calories than the snacks that put the weight on me. btw, one of those snacks involved a triple chocolate ice cream with m&ms on top and chocolate syrup. instead, now it's a chocolate protein bar or low calorie brownies or hershey's zero sugar mini bars.

For normal variation, I can easily see a 4lbs difference from one day to another. The reason? Eating more salt in combination of mild constipation, or airline travel. some people experience the same in various parts of their menstrual cycle, starting a new workout, sleeping poorly, storing more water in their legs during a workweek at a desk, and thousands of other reasons. None of them have anything to do with fat gain. All with temporary fluctuation of water or poop weight. And yeah, this can totally mask weightloss. It's just what it is. That's why it's a good idea to wait at least one full menstrual cycle to re-evaluate whether you're losing weight or not, if you don't have a lot to lose even more than that. Understanding these fluctuations is one of the keys of not giving up.