I think that u will strain your self a bit too much if u do psych and history for A2 and sit the AS exams. I think you shld carry on with computer science and try as much as u can. Also, psycholoy and history are essay subjects and they r VERY HEAVY CONTENT so it will be veryyyyyy difficult for u. Do what u think will be right for you but speaking from a Y13 perspective i think that u shld just keep ur subejcts