There could be various reasons why you might be struggling to gain weight, such as a fast metabolism, inadequate calorie intake, or even underlying health conditions. To start, I recommend keeping a food diary to track your daily intake and ensure you're consuming enough nutrients. Including protein-rich foods like lean meats, nuts, and legumes can help build muscle mass. Additionally, incorporating healthy fats like avocados and olive oil into your diet can boost your calorie intake in a nutritious way. If you continue to face challenges, it's best to consult with a nutritionist for personalized guidance.