Your in the exact same situation I was in last year (apart from i did media instead of economics).
If you do medicine you have to take a UKCAT test, which tests your personality, and if it is suited to the job, so not just your grades are taken into account. To do medicine you need to be really passionate about it, when I was considering doing it, I was told to volunteer with old people because the universities look for compassion in you, and that will look really good, as well as improving personal skills.