I'm in the same boat as you right now, feel like I have completely flopped all of my exams despite revising a ton. So I talked to my teacher, she told me that it is possible to come out with good grade, but it will take everything you've got. Basically told me that once I get into year 13 I'm going to have to work independently, after every lesson summarising what we've learnt in a mini booklet. That way by the time revision for exams comes around I'll have a solid background. For now all I can say is that I'm going to try and stay positive about my remaining exams and try and do the best that I can, at least then if I get a D then it will be a high D, making it easier to push up my grade at A2.