Wingy - If the issue is just your gpa, you have two years recover it, although I think "recover" might be too strong a word. But if the issue is that you're worried about how much commitment this is going to take in terms of time, energy, money and steely resolve, then a little soul searching is probably in order. In fact, even if you aren't worried about those issues, a little soul searching is in order.
You're gpa probably won't keep you out of medical school, (although it will if it gets really low), but a lack of motivation will. And sometimes motivation involves continuing even when you think it's hopeless, and continuing even when you think you just can't do it anymore. Most of the time it means putting one foot in front of the other, and doing the very best you can in every area of your life.
You have at least two more years to go. If you want to be a doctor, it may mean additional years of school via post-bacc, or taking a year off to do research. If this is what you want, you'd better be willing to do what ever it takes. But think about this carefully...
Nanon