where are you doing your A levels? if you've done physics up to AS, that should suffice. get the basic idea of pressure, water potential gradients, etc

well, i'm guessing you like the physiology and biochem parts of biology. as you may have already noticed in A2 you'll learn the bigger aspects of biology like natural selection, biodiversity, crop plants, etc which has near NOTHING to do with medicine. but its good that you like biology, which probably means you like reading and you are looking for a career which involves life long learning. what your teacher says isnt actually true, i know plenty of medical students who took bio chem maths and for their fourth subject they take either psychology, economics (me included), english literature and to a certain extent history or accounting. but there is no doubt a sound foundation in physics would help in the long term later on in your pre-clinical years.

its quite difficult to get work experience here in malaysia for medical students, it'll take a looooong time for you to get a placement if you use the proper way of sending a formal letter to a government hospital. private hospitals are too tedious when it comes to protocols. i did mine in a government hospital in a rural part of town, they've been known to be more cooperative. it also helps if you already know a doctor, that way you could just ask him/her to settle a placement so you wont have to wait so long. its better to do your work experience at a hospital than at a clinic, you'll get to see a wider variety of cases (depends on which ward you are attached to) and you will get to experience the ever tiring life of a doctor.

i did my attachment in terengganu which is a far way from sri hartamas
i'm not sure about that because monash malaysia isnt exactly monash australia. if you want to work in the states i suggest you try applying for IMU's partner medical school twinning programmes. you can complete your clinical years in the US/UK/Australia and you would have a better chance of working overseas.

hospitals do allow A level students to come and do their work experiences, it's just a matter of which hospital would have the time to entertain you. you have to remember that hospitals are a busy place.

exeter got MBBS ah?