You’re definitely doing more than enough at the moment, I did not even half that and got an offer for med,
The amount of experience isn’t as important as the ability to reflect on what you’ve done and relate it to medicine
Regarding doing the 4th A-Level, I personally wouldn’t, sure you can get an A* but as someone who does Spanish A-Level it’s still more work to fit into your timetable, writing and presenting your IRP, writing essays, etc it’s more work than just being able to speak and write the language if u get me?
It may affect the amount of time you can spend on your other alevels and could affect those grades, for med I don’t recommend doing more than 3 alevels to anyone tbh, coming from someone who does 4 and regrets it lol, I would realllyyy recommend just focusing on 3 and getting the highest grades possible