Honestly, with just those 3 alevels you have a lot of potential, so I'm afraid I won't be any good at helping you narrow any career choice down. However, from the top of my head, these are definitely some areas where you could excel:
Government and public policy Law Education Mathematics Journalism Research Business Management Finance
These are just a few of the areas that you could go with your chosen subjects. Bear in mind, you could do a combination of these as well - you don't necessarily have to bind yourself down one select career path if you so choose. After all, it's more dependent on your skills and interests.