A Levels are really tough going and it can seem like its the most important thing in the world. If i could go back in time, I would tell my younger self to just relax a little bit more. Have you ever tried yoga or meditation? Its a great way to relax your mind and allow you to focus on what you think is important. You will be able to revise much better I think if you do take 20 mins a day just to meditate. I know it sounds a bit hippy and mad but it really does help. I know you can feel under a pressure and faced with too much work which in itself can make you feel overwhelmed but just take a deep breath.......
Good luck! x