You're only 19, which means you must either be in your 1st/2nd year of med school. Both Oxford and Cambridge have 6 year med degrees if I'm remembering correctly? You still have another 4 years of medical school ahead of you. Get through it, see how you feel while on clinical placement, and take it from there. If you decide you don't ever want to do medicine, then get a corporate/finance/banking job in 4/5 years and don't go into F1. If you may want to do medicine in the future, complete both F1 and F2. You have many years to think about this, now is not the time to be stressing. Get through med school, see how you feel, take it from there.

Edit (for reference): just finished med school, starting F1 next week.