Learn to live more in the present moment, by using the progressive muscle relaxation, in section 11, at ezy build, below. Set yourself a specific time period for worrying about anything, (say; around three quarters of an hour, possibly when you get home, or after your evening meal, but not too close to bedtime) after which, resolve firmly to refuse to even entertain the thought of worrying again on that day: realise and accept that to do otherwise would be counterproductive to your mental health, and enjoyment of life. You will have had your "worry time" for the day, and can just write down any more thoughts that come to mind, and say to yourself: "Well, I'll just have to worry about that tomorrow, won't I?".
See study tips, memory improvement, (and find out which is your learning style, and adapt accordingly) at http://www.ezy-build.net.nz/~shaneris in sections 13, and 41, and start study/homework groups with friends. Take 4 Omega 3 fish oil supplements, daily: (certified free of mercury) it is best if consumed with an antioxidant, such as an orange, or grapefruit, or their FRESHLY SQUEEZED juice. If vitamin E is added, it should be certified as being 100% from natural sources, or it may be synthetic: avoid it. Scholastic achievement is only one pathway to success, and many people are just not suited to that path, so don't stress too much about it. See: "For Most People, College is a Waste of Time" Enter this in the searchbar at http://www.mercola.com/ Richard Branson left school at 16; Winston Churchill was not a well-performed student, and Bill Gates didn't finish college.
Your future may well be in another field, such as: graphic artist, real estate, cinematography, Feng Shui consultant, landscaping, fashion design, aromatherapist, music industry, photographer, personal trainer/aerobics instructor, etc. School is about teaching some basics, and keeping students occupied, so adults can work, that's all! Try many things (except drugs, binge drinking, and the more dangerous ones) and develop those areas in which you perform well, or have natural talents.
Consider having aptitude tests, vocational guidance, and career counselling, to give you some ideas on what may suit you best. Ultimately, it is much more important that you be a good person, who helps others when reasonable to do so, and makes a fair contribution to the society which supports him/her, than academic performance. Weight loss is addressed in section 56, at ezy build, and stress, in section 42; see page i first. Depression; section 2; see page R first. Also see male depression, teen depression, and eventually the rest of section 2. Take the quiz, in page J; print, and take to your school counselor, and/or make an excuse, and show to a doctor.