Oho, I don't mind, to be very honest - but PP can be a pretty tight knit community.. which is why I'll hold off answering that question (just dont be offended, or anything!

)
Let's just say its very cold, here
Pre-med is tougher than Commerce-based subjects (that I had).. Anyhow, about exams, all I can say is that the time is gone for learning (for most part) - now its all about perfecting your application. I say ditch the books and master those past papers, as many as you can.
For my A level accounting (God, how I hated that subject) - our book contained pastpapers from the 1980s, and we pretty much did them all. 2 weeks before the exam, my teacher emailed us some 20 extra practice questions from ACCA exams. Needless to say, majority of the class aced it (even though Accounting is one of the toughest subjects to write in A levels - and the rumours are true: Accounts paper 4 is at times, technically incorrect.. so there).
But do allow yourself some breathing room. I'm not sure if it works for everyone, but I personally require some down time before an exam to gather my senses about me. Over-preparation has let me down more times than I'd like to say (in fact, Pak Studies [specifically Geography] was one instance where I messed up even though I knew everything).. The aim of the game is to assure yourself you know everything (which you probably do) and that you can handle anything thats thrown at you.
The fact that you've taken so many exams that you feel used to it - I think thats great. Completely puts off exam pressure, and helps dealing with nerves.
As for when you are practically sitting in the hall, taking your exam - and you feel tired and exhausted in the middle (like I did today's exam, in the middle of my 21-page marathon) - just buck yourself up immediately. Remind yourself you've toiled so hard for this moment, and it's all under control - you will
not let it slip away like that. Time management is everything in O/A levels - you get that right, you're practically in the B+ category..
Aw man. Now I miss my O/A level days.... :'D