Do you mean that your doctor doubled your dose before the summer or recently whilst you've been trying to revise? If you haven't already, I'd suggest going to the doctor and explaining the problem and the fact that you don't think your increased dose is making a difference. Changing your dose/medication now obviously will probably not have an effect soon enough for your revision, but a doctor may be able to offer different types of solutions, and in any case a medication or treatment change might help in the long run (although it might be worth considering that any drastic changes with unknown side effects shouldn't really occur so soon to an exam period!)
As for other advice:
Have you tried revising with a friend? They might help motivate you, and it would be an incentive to get up if you agree to meet at a specific time. Maybe change your revision style or where you revise? For some people, it might be easier to revise if you go to a better environment like a library, or just a quiet place in your house. Once you actually go there, the main motivation obstacle is conquered, since the environment can help with motivation. For me, I actually prefer revising in my room and have recently started doing this - probably a comfort thing, and seems like less of a mountain getting up to my desk etc. Maybe surround yourself with motivating reasons to work (positive ones rather than ones based on fear).
Good luck!