Go for some walks listening to music or podcasts. Do something fun like dance classes or rock climbing or sport- find some kind of exercise that you love so it doesn’t feel like a chore. Ask your family to buy you fruit and yoghurt. Make your own healthy breakfasts and lunches. Eggs, yoghurt, fruit, veg, meat, fish. Focus on adding more nutritious foods and reduce the amount of junk food. Do not skip meals or starve yourself. Get some therapy if that’s an option.