Tough luck, my friend.
I'm taking my 'O' levels this year as well, but it's at the end of the year. Just finished my Mother Tongue paper yesterday. You guys call it Cambridge International Examinations? We call it General Education Certificate here, haha.
Well, back to topic, ten days for three subjects is quite difficult... I take History as well, not sure if I study the same things as you, but if you spot topics, which mean to focus on topics that you think may come out according to previous years' tested topics (e.g. 2008 - Nazi Germany, 2009 - Communist Russia, 2010 - Fascist Japan, 2011 - Cold War, 2012 - War in Europe, 2013 - anything except for the previously tested topics), it'd be a lot easier. Of course, it's always better to study everything.
Here wishing you good luck, your efforts will pay off! :pop: