Hi! I'm glad to hear that you're interested in studying medicine. It's a great career choice, and I'm sure you'll be a great doctor.
As for your fourth A-level, it's a tough decision. All three subjects have their own merits. Physics is a good choice if you're interested in engineering or other STEM fields. Further maths will help you with your maths A-level, and it could also be useful if you decide to study physics or engineering at university. German is a beautiful language, and it could be useful if you want to work in Germany or another German-speaking country.
Ultimately, the best choice for you will depend on your interests and your goals. If you're not sure what you want to do after you finish school, then it might be a good idea to take physics or further maths. These subjects will give you a broad foundation in science and mathematics, which will be useful for many different careers. If you're more interested in German, then that's a great choice too. Learning a new language is always a valuable skill.
Here are some things to consider when making your decision:
Your interests: What are you passionate about? What subjects do you enjoy learning?
Your goals: What do you want to do after you finish school?
Your strengths and weaknesses: What are you good at? What do you need to work on?
Your time commitment: How much time can you commit to studying for A-levels?
Your school's requirements: What A-levels are required for your chosen university course?
Once you've considered all of these factors, you should be able to make a decision about which A-level to take. Good luck!