Have you told your parents? If not, be sure to let them know that you are feeling down and you want to talk. Another idea is to think happy. Think about your best friends and all the happy memories you have. If you have a crush, try thinking about them too👍🏻
Why are you sad? If you want to feel happier I suggest listening (or dancing) to super happy music, going on a shopping spree, binge-watching your favorite tv show, or putting on your favorite outfits and having a fashion show with them.