dropping a subject

I'm currently half way through my as levels ands my mocks are in a week, I've been getting really stressed out with my subjects because I stupidly took 4 of the hardest subjects there are...Maths, History, Philosophy&Ethics and government and politics... I'm struggling with the work load and suggested to school I dropped government and politics because I'm not enjoying it at all anymore and I'm struggling most in it, I'm stressed to the point where I'm not sleeping at night. My 6th form should let me drop it now shouldn't they? Please help if you have any advice it would be much appreciated