If you've had reasonable portions (which it sounds like you have) then you are not actually hungry. You don't need ant more food.
There may be several things going on and the solution will differ depending.
Tired - studies have shown poor sleep increases feelings of hunger (but not food need). Solution is to get enough sleep. Exercise and sleep hygiene will help with this.
Thirsty - drink a glass of water or cup of herbal tea whenever you get the urge to snack. Gives you something to do with your mouth. After a few days, you should be able to differentiate better.
Sugar - eating too much sugar and simple carbs (sliced bread, breakfast cereal, white rice etc.) will give you an insulin spike which will cause feelings of hunger an hour or do later as it subsides. Solution is to avoid simple carbs and sugar for a week to reset which will feel terrible but really pay off. If you incorporate back into your diet look for tips on reducing the spike e.g. eating leafy veg 30 mins before.
Hormones 1 - be mindful of the time of the month and whether this affects your eating patterns and cravings. If so, plan for it by having appropriate snacks available and maybe saving up a few hundred calories at other times of the month.
Hormones 2 - hunger is controlled by ghrelin and leptin hormones. These can be affected by various things including a diet high in ultra processed foods. Studies have shown increased hunger hormones even straight after eating when test subjects have eaten lots of upf over a few weeks compared to levels before the diet change. Best solution is to eat mainly whole foods where possible.