Based on your age what I am getting is that you are just completing your teenage. This is the age where a boy is preparing to become a man. There are choices to make about career and the life coming ahead. Sometimes these constant running thoughts of life and career can play it's part causing these adverse conditions. What I recommend is think straight, eat healthy, study with heart if you have made the choices in whatsoever field, get indulged in some physical workout like jogging, swimming, cycling or some sport of your liking...And that's all, nothing to worry about anymore. This is a mere lifestyle modification technique to overcome stress.