Pick a major that interests you so you don't mind devoting a majority of your hours to studying. Your major is not as important as your undergraduate grades, your MCAT score, your letters of reference, and your personal statements on your medical school application. For now, just focus on finding a college that fits you and your budget and a major that really interests you in college so that you will make great grades and get strong letters of recommendation from professors that recognize your potential.
A medical degree from medical school is another 4 years of education.
In order to get a degree in medicine (I'm assuming you mean to become a medical doctor) you will need to earn a four year bachelor's degree from an accredited university. From there you will need to get a four year degree from a medical school. The last step is residency, which can take anywhere from 3-7 years. So in total, you're looking at 11-15 years in total.