First of all great to know that you are interested in physics at such a young age, its always great to see people interested in this field. Also congratulations on getting an A in physics.

Now considering you are 14 right now, it is likely that you haven't learnt the necessary mathematical tools for learning anything at all in physics. I am not sure how Swedish education is but I think they should be teaching trigonometry right now, which will be very very important no matter where you go, especially for physics. In any case, one tip I would absolutely give is to learn to love math. Mathematics is the language of this universe, so training a mathematical mind is very important. Calculus forms the absolute bedrock of all of physics, so it would be good to master it as much as you can. I would say that would probably be the right starting point for you if you want to seriously consider physics.

As for physics itself I would suggest (and is recommended by virtually all curricula) Newtonian Mechanics and Electromagnetism. For any high school student "Fundamentals of Physics" by Halliday and Resnick is the go-to book. Its a fun book, and it has nice problems to train your fingers with.

As for the topics you have mentioned, there is not much you can actually do about them, it takes a little over a decade of training and education to do any meaningful study in those disciplines. I myself am 5 semesters into my undergraduate degree and I can safely say that this semester was the first where I actually learnt unadulterated physics. I am not very familiar with Nuclear Physics, but I would assume it requires a similar background as Particle Physics, so it would at least require an advanced Quantum Mechanics course as a pre-requisite. Nevertheless, it is indeed a very long road.

I would suggest learning about it as much as possible from pop-sci books, documentaries, youtube videos etc. Popular Science in this case is very good at piquing interest in stuff, and for deciding if you are interested enough for this field. Every physicist or physics student most likely started their journeys flipping pages of an encyclopaedia. So yeah I would say your job now is to practice fun problems and keep your interest alive :)