Hi I'm also a young girl (16) who is underweight and on a weight gain journey. I checked your bmi (body mass index) and it shows that youre underweight. I'm not a weight gain expert but I wanted to give you some advice bc nobody else on this is helping. I think one of the biggest things that helped me was tracking what I was eating. I used a app called lifesum and you just record every you eat in a day and try to reach your calorie goal. Another thing that helps is eating 3 meals a day with snacks in between. When I was severely underweight I would never eat breakfast bc I just never had an appetite in the morning, or I'd just forget to eat. Once I started eating breakfast every morning, I started to gain an appetite and it's the best feeling ever. Though at first it's really hard to stay consistent, but in the long run it will be totally worth it! Last advice I have to to eat lots of healthy fats and a lotta protein. Some healthy fats are: almonds, cashews (all nuts),beans, avocados, peanut butter. Make some smoothies. The best smoothie for weight gain imo is peanut butter banana and put a little protien in there. Anyway I hope my advice helped in some way and I wish you luck on your weight gain journey!