5"2 18 yr old female who struggles to gain weight despite eating a lot. Now that I'm trying to have a healthy diet I've started losing weight?

Do not worry. you have that special metabolism that burns calories despite eating anything you want. the most important thing you can do is eat a balanced diet, exercise modestly and get plenty of sleep. avoid energy drinks and smoking to ensure optimal health Don't worry as you get older a slower metaboism will probably appear and you will wonder about how you can avoid gaining weight.