I train regularly and pay attention to a healthy diet. Despite this, I didn’t lose any weight and actually gained it.

It’s possible to gain weight due to muscle gain when working out, as muscle is denser than fat. Consistent resistance training coupled with proper nutrition can lead to an increase in muscle mass, which may offset any reduction in fat mass, resulting in a stable or increased overall body weight.
Despite maintaining a consistent exercise routine and adhering to a nutritious diet, the lack of weight loss and subsequent weight gain could be attributed to various factors such as metabolic rate, portion sizes, or hidden caloric intake from snacks or beverages. Additionally, stress levels, sleep quality, hormonal imbalances, or underlying medical conditions could also influence weight fluctuations despite efforts to maintain a healthy lifestyle. Consulting with a healthcare professional or a nutritionist to assess these factors and tailor a more effective approach may be beneficial in achieving desired weight management goals.