You may have to slow down your pace. You might discuss dropping one of your outside lessons or activities with your parents or ask your guidance counselor at school to help you sort out your priorities. If you can't change the cause of your stress, then try to reduce the way your body reacts to stress. All stress reduction is based on finding a good way to relax. The answer is to find some non-drug way to lower your sense of being stressed.
Some people sit quietly and watch birds or flowers, some use meditation.
Some join a religious group. Many people, young and old, find that exercise is the perfect way to help them lose stress and sleep better. Find what works best for you. Reading is another good way to get rid of stress. If you can identify a special problem that is bothering you and causing you to be stressed out, ask a librarian for books in which a young person deals with a similar situation.