It sounds like you are asking about career options with various college degrees. The options are pretty much limitless. For example, just doing a quick google search for
careers with an english degree reveals
this page which includes a long list of career options for people with english degrees. You can see how many different things can be done with an English degree. The options are similar if you look at almost any other field. I think it probably makes more sense to start with what things are of interest to you and then narrow things down from there. The good news for you is that you don't need to select a major for a few years.
If you are considering medical school, you can start out taking the required pre-med courses and any other college requirements. You can use your elective time to take courses of interest to you. You should discuss your interests with your advisor at college to get ideas for coursework that would best suit your interests and may also help you decide what you would want to do for a career if the medical school route doesn't pan out. I think the important thing to discuss with your college advisor is to select the courses that will give you the most options until you have a better idea of what you want to do. If you are passionate about music performance and you have the skills to pursue a career in that field, you should give yourself a chance to follow your passion. You don't want to always ask "what if" later in life. I have always believed that when it comes to education and career choices, keeping your options open is the best choice whenever possible.
As for becoming a teacher, there are different requirements whether you want to teacher kids or college level students. I know that you can study to be an elementary school teacher and get a bachelors degree and meet any state licensing requirements, or many people go back to get a Masters in Education after obtaining a bachelors degree in a field other than teaching. The Masters in Education programs are designed to meet the state licensing requirements. For college leve teaching, I don't think there are state licensing requirements, but you would have your best chance of getting a job if you have either an advanced degree or significant experience in a particular field (which obviously you wouldn't have coming right out of college).