According to the symptoms (excessive sleepiness, unpleasant thoughts like: “my life sucks” or “my life is not worth for living”) you could be experiencing depression. Decreasing your body mass. can definitely help you to improve your physical health and probably your mental health. Also, you can seek treatment for depression from a mental health professional. Depression can be typical for students your age (15) at a period in life that can be confusing and overwhelming. But you are not alone! If you are ready to seek help, you can start by asking a trusted adult about community resources in your area where you can find treatment alternatives.