Hi Sunny,
Just so you know, it is not at all necessary for you to make up your mind at this point in your life. Many applicants to medical school don't even have their "dream specialty" nailed down - often, medical students make this realization after matriculating, even as late as during their clinical/clerkship years. So you, as a Junior in HS, certainly don't need to narrow anything down yet**
That being said, you can begin looking for various ways to get involved inside the hospital (as actual exposure really is the only way to make an educated, tentative decision). Look for volunteering opportunities at your local hospital. Reach out to physicians for potential shadowing opportunities. Stay updated on "movements" within the field, whether it be research, policy, or educational shifts. These sorts of things will help you become more educated about the various different roles that a physician can play and, potentially, help you realize which particular niche you see yourself in.
Finally, to echo radkat, make sure you take the time to slow down to enjoy your final years of HS and college. It's a cliche, but you really will never get this time back. Don't burn yourself out just to get to med school, only to realize that you'll never be 18-21 again.
**This is just a personal (n=1) opinion, but I think that it's extremely unwise to try to force yourself to narrow down your options at this stage in your life. Perhaps thats not how you intend to sound, but it's how you come across. "Liking the idea of a job in the medical field" is enough for now. Do NOT (again, in my opinion) just blithely, almost casually, pick neurology or neurosurgery because it sounds impressive. Every time a freshman tells me that they want to do neurosurgery, I ask them why. It infuriates me (strong word, perhaps "irks" is better) when they just shrug and say "it sounds cool." Get a strong idea of what each specialty entails, the lifestyle, typical cases, etc before you set your heart on anything. And that, I think, should take you several years to accomplish.