Can anyone give me tips on this...?

I keep feeling sad and angry all of the time. I know it isn't exactly rare for a girl to be like that, but I hate it and I fell as if everyone is going to start hating me because I can't control my feelings. I always try to look for the positives in life, but at the moment I just feel like crying all of the time. Please give me tips on how I can stay focused in school and not burst out in tears xx thanks