I desperately need to relax, im only 15?

Maybe writing a journal or something might help= sometimes writing everything down can clear the mind. Also listening to relaxing music and having a hot bath. Get a check for anaemia. Also make sure you DON"T fall asleep after school. Force yourself to stay awake- go for a walk or do something active. Then you will be more likely to get good quality sleep at night. Also have a look at your sleep hygiene- make sure you don't do anything stressful before sleep. Google 'sleep hygiene' and it will give you more tips.