Stop saying "I can't," and start saying "I can." When you put your mind into doing something, such as your science homework or maybe that media essay, tell yourself that you can do it! Many studies have shown that thinking positively about hard tasks and homework is far more likely to get you better results than thinking negatively about something.
Start surrounding yourself with positive minded people. Whether this be a few blogs on tumblr that post inspiring and uplifting posts or making a few new friends, it's important for your mental health to be surrounded by people who are able to motivate and inspire you in improving you school life.
Setting realistic goals is key! Staying positive during stressful times, such as school, doesn't mean you have to become a super hero. Be realistic with yourself. Discuss with your teachers, parents or someone you trust about your school goals and make a plan on how you can reach them.
Basically, staying positive is a pretty big deal. It may take a while for you to get into that mindset, but trust me, it shall all pay off in the long run,
Just one more thing, if you are stressed about school or college then please remember to breathe, tell yourself it will be okay and carry on. There are plenty of people that really want the best for you and are willing to help at any time.
Love you all,
P.s. Keep your head up, you can do it. I believe in you.