On some of the days you might have felt very tired, less hungry, more irritated or cranky. All these behavioral shift from your normal routine is most probably the effect of hormonal changes on those days. Hormones are chemical substances than traverse through blood to different parts of our body and regulates our emotions, behaviors, physicality and psychology.
Slight variation in these hormone levels can have a huge impact in our day-to-day life. For example increase in cortisol (hormone responsible for managing stress) can increase blood pressure, cause anxiety or drain us out quick making us feel tired. They also increase our blood cholesterol which in-turn bloats our body with bad fat. Insulin is another hormone that manages the carbs and fat metabolism in the body and its variation from the median can have adverse effects like losing/gaining weight.