You can major in almost any subject and still be Pre-Med. Pre-Med means you are preparing for medical school. To apply to medical school, you have to take certain classes in college. Many of those classes overlap with the classes you need to take for a Biology major, but you could study something different, for example, English, and still take all the Pre-Med classes and apply to medical school. Some colleges offer a "Pre-Med" major, which I believe includes all of the required classes for application to medical school and other classes related to medicine. Either way, you still have to go to medical school after college to become a doctor.
Typical medical school prerequisites include:
Biology: Lecture – 4 semesters; Lab – 1 semester
General Chemistry: Lecture – 2 semesters; Lab – 1 semester
Organic Chemistry: Lecture – 2 semesters; Lab – 1 semester
Biochemistry: Lecture – 1 semester
General Physics: Lecture – 2 semesters; Lab – 1 semester
Math: Statistics – 1 semester
English: Rhetoric (Composition) and Literature – 2 semesters
I chose biochemistry as a major because it overlaps with the premed requirements and I was able to obtain my bachelor's degree in 3 years.
A major in biology requires different classes.