start my own buisness

I am thinking of given up this one because i have chosen a career path. I want to study zoology. Though I may do this a few years down the line. Who knows.

I’m nearly 17 now and am still finding it hard to chose a career. I’m studying AS levels at the moment. Whenever someone asks me what I want to do I say I don’t know but when I think about it, when I really think about it I want to start my own buisness. The trouble is though I have no idea (or money) of where to start.
The Alevels I am studying are biology, chemistry, physics and history and I plan to drop physics next year.
I have no idea where to go with this.