Dear young friend. I did share your interest in physics and I was not bad at school. i think the way the Khan academy proceeds in physics is a good option and I would be you, I would follow their path. The same applies to mathematics. So far to the rational way to proceed. Emotionally physics was and is for me a fascinating science and dealing with it opens our sense for what our current science is finding out about it. Forget about quantum physics and relativity theories from your learning of physics. Look for good videos in youtube and find some that speak in a more general public kind about those fields of science. That puts you in touch with those topics and you can start to reflect about what you find interesting. With mathematics the way it is taught at school and which you will need to master your tests in mathematics at school the Kahn academy gives you solid information to learn. But as with physics, where there are topics that you need at school in which give you a starting point, mathematics offers at least equally fascinating topics that equal in opening your eyes for a whole new way to see the world around you. i f you allow me, I would to tell you a bit about what I mean! I did finish my studies at a technical university in 1979. That was then the last time I had to deal with mathematics in the way I did learn until then! So nearly 4 decades later the science about mathematics has also been developed very heavily. The mathematics as you learn to the end of high school really is not mathematics but is learning to apply formulas to solve equations. The top of this king of "mathematics" goes and includes calculus. Terms like differentiation and integration are ones that you can search via google and find information about it. I like very much the current definition about the science of mathematics. Mathematics deals with finding "structures"! There is a course from the Standford University which can be taken for free here: "Introduction To Mathematical Thinking" This course has the purpose to help students to make the transition from the kind of mathematics they have been taught until then and to the kind of mathematics the students are required to learn and apply at the university. Do not let yourself be intimidated. Its even more! As you have not yet been spoiled to think the traditional way mathematics was done until about 200 years ago, you will probably have it easier to grasp this "Mathematical Way of Thinking! If you listen to the lecture of prof. Kevlin that you can see as videos, if you listen to the videos were he very detailed explains interesting topics as help for solving the challenges to think the mathematical way, you could have it easier than older ones to capture what is being taught.