I am a med student so let me give my inputs. Anyway Chem and Bio
combination is not only preferred, its is the only way to get in.
There have been students taking Phy and Chem getting into Medicine
but I can affirm you that their chances are extremely slim.
That's bad news for Sg students interested in Medicine, seeing how
problematic (ie. screwed up) the H2 Biology syllabus is.
Generally, Physics and Chemistry at 'A' levels is still a far wiser
option (than Biology and Chemistry), in terms of
availability/number of University level courses open to you.
Afterall, you (all students) may change your mind about
studying Medicine one day, and you'd want to have as wide as
possible, your options of available University level courses.
To Shinsyuen, where there's
a will, there's a way. You could always study Medicine in an
overseas University (eg. explore scholarship options if finances
are a problem).
Still, given your career dreams, it's
definitely better for you to take triple pure sciences now at
secondary school level. You probably want to transfer out of your
current school if they refuse to let you take pure sciences. Try
getting your parents to appeal to the principal first.