When you say you have to stop being unbelieavably lazy you have to mean it. And that does not mean put in 100% more work, because if you were lazy that means you did very little I am assuming, so you have to crank it up like 1000% more work, dedication and effort. Getting into a routine helps. For example when you come home do you watch tv or do you do homework, write essays, read ahead in the book?
Your strength seems to lie in less mathsy subjects like Geography and Economics. I would stick to subjects like that and drop maths and physics completely. I am saying this from the point of view that I did physics myself and I just got U's in my A2 exams when I got a B at AS. A2 physics is 10X harder than you would believe and I gave up everything to study for it.