I'm not a medical student. In fact, I'm not even a pre-med student. But I am a bit older than a lot of the people on these boards (late 20's), have a successful career in a totally non-medical field, and am considering quitting it to go back for med. So I will give you some advice that I wished somebody had given me when I was entering college.
The advice is this: cliche as it sounds, you really can do almost anything if you work hard enough at it. The people who make it in pre-med are NOT the smartest, but the most determined. I had a ton of friends in college who started pre-med and by sophomore or junior years were so sick of all the work involved that they dropped out. Few of my friends ended up even applying for med school. As for myself, I briefly considered the idea, but as a freshman I took one look at how hard pre-meds worked and decided that I didn't want to spend my college years like that.
The upshot of all this? Explore medicine thoroughly. Do some volunteer work, arrange to shadow a doctor, read some books on the subject. Because if you find out that it's TRULY what you want to do, then you will have the motivation to grind it out and you WILL make it. And if you find out that it's not really for you, you will have a much more enjoyable experience in college by not putting yourself through the torture.
Finally, a lot of those pre-med friends I had who didn't end up going for med school suddendly decided around senior year that they were going to law school instead. Few of them are happy with that decision now. The trap that a hell of a lot of college kids fall into is not realizing that there are literally tens of thousands of careers out there. They think "if I'm not in law school or in med school, what will I do with my life?" What they don't realize is that, sooner or later, most people will fall into something good. It just happens that way. Me, I'm in a career that I never anticipated I would go into, and I actually have done quite well with it, and in many ways like it (even though I am thinking now that, long run, I might want to do med instead). So, whatever you end up doing, don't think that you have to go to a professional school to have a good career. Be honest with yourself, believe in yourself, and make your choices for the right reasons. Things will fall into place in ways you never expected.
P.S. Most importantly: have FUN in college. Drink beer, date, do some silly stuff. If you don't you'll regret it.