Are you sure you actually want to be a doctor? Or do you just want a doctor's salary? You can come up with all kinds of excuses (I like science, I want to help people, etc), but you really need to objectively analyze your motives for the career choice. If political science is what you have more passion for and a field you can actually see yourself having fun in then why not just go for that?
But as for the question about double majoring - it isn't even necessary. Medical schools aren't too particular about your major, they accept anything from theatre majors to economics. Just get good grades in whatever major you choose, and make sure you complete all pre-med classes on the recommended timeline (Chemistry, Organic Chemistry, Biology, Physics, etc)