What to do for my career?

I'm in a bit of a problem.. I am at the stage of my life where I have to pick appropriate subjects for my future life/career.. At the beginning of this year I wanted to pursue acting or photography... Something "creative" and I had wanted to at the time for 2 years.. So I was going to pick subjects such as English, math, photography, drama, media studies... And then I went to wanting to pursue medicine, specifically a doctor.. So I chose my subjects as English, math, physics, chemistry and biology.. The thing is, recently I've wanted to go back to acting.. And I know this sounds like a stupid 16 year old girls phases.. But I really feel like acting is right for me.. And I'm sure 35436436436 other people do as well.. But its like I have a real calling for it... My mother recently spoke to my drama teacher from this year and she told her that I definitely had real potential for a future in acting if I wanted to... And that really made me want it that bit more.. What I'm asking is... I dont know what to do... My father is really proud that I want to pursue medicine.. But the thing is... Thats pretty much 8 years before I'd become a qualified doctor.. And to me thats a really long time... And I know theres no gurantee of a job in acting, but ... Ah... What would you do if you were in my situation?? I want to go into screen acting by the way.. :) Thank you!