Hey 13 year old, If vegetables are hard to eat, just eat at least one vegetable a day. Don't like a type of food? Try one bite of that food at the very least, and see if you like it. Just for one each day. Then over time, you'd find out what vegetables you like.
Hey 13 year old, Some basic ways to improve your physical health is to learn about the basics of the science of nutrition, such as the different vitamins and minerals, as well as what food has each. It's taught in school, but almost everyone forgets it.
Hey 13 year old, If you want, you can look for "exercises for kids," or "fun exercise games," if you want a way to get moving, especially if you can't sit still. You can look for a lot of indoor workouts and exercises for kids, as well.