I am only a little older than you, but if you want to be a doctor, be a doctor. Paramedic just adds 2 years of school and another few thousand in debt if you are only wanting certification and you will have enough of that anyway.
I thought I wanted MD until I researched the time involved to get to that point. I started looking at PA after that, but I was just hating my math/science classes in school. I jumped ship to my schools Fire/Paramedic program and have loved it. On the other hand, I plan on enlisting after college and have my whole life, so my pay is going to not be the most exciting no matter what side (mil/civ) fence I'm on and I have always known that. I do plan on PA school down the road, but I just got burnt out with struggling in school and all the useless stuff I am required to take and this major finally gave me something I am actually good at and that I love doing.
Honestly though....you're 18. That was 3 years ago for me and a lot has changed in my life in just 3 years. I've had a lot of good things happen and things I partially wish I could just forget. I've moved states, almost gotten married, lost some pretty important people, and just done typical college stuff. A lot of this stuff has changed what I thought I wanted to do, I never would have guessed I'd be taking Paramedic classes even just 2 years ago. You have 2 years of (I'm biased since I don't like most of them) useless classes ahead of you. Plenty of time to get some experience of what lies ahead of you and you might find what you want changes.
Just go into college knowing that what you want could change. Be a good student, work hard and don't be an idiot. Once you get close to the point your classes are more focused, evaluate where you want to end up. If it is MD, then charge on and kill it. If you decide that isn't for you and Paramedic is what you want to pursue, sign up. For now, enjoy your first year of college as you learn to adjust to the changes it brings, you will get you answer soon enough.