Hi Karen, I love your question because I had the same interest when I was your age, which was almost 40 years ago. I was interested in becoming a doctor, so I sought out opportunities to interact with anyone and anything in the medical field.
I was fortunate to obtain an after school job working for a veterinarian all through high school. Although this wasn't working with human medicine, it provided exposure to medical procedures and eventually allowed me to assist during surgeries, helping the doctor in ways that would not have been possible during human surgery. So consider applying for a staff assistant position with a local veterinarian, even if would only involve cleaning dog runs and cages. If you're dependable and get along with the other staff, you will find opportunities for exposure to many of the same procedures used with human medical treatment.
Another suggestion is to become a volunteer at a local hospital. Most hospitals have volunteer programs intended to help medical staff and patients. The federal HIPAA regulations may limit the amount of exposure you would have to actual medical procedures with patients, but serving as a volunteer can give you a wealth of information about how hospitals function and the various technology areas that might interest you within the medical field.
Lastly, consider speaking with your school nurse about your interest. They will probably have some helpful suggestions that are specific to where you live and go to school.
You're asking all the right questions for someone your age who is considering a career in medicine. That's fantastic and sets you apart from so many other people thinking about their future career! The more you know about medicine the more you'll be able to decide if medical school is a good fit for you. Medical school is expensive and the training takes years... but the result is professionally rewarding and a great benefit to society. And if you ultimately decide not to pursue medical school, you can still find many alternative career opportunities within the healthcare field.
I'm impressed with your question and I wish you great success as you continue your investigation!