Flip a coin.
Heads is Maths
Tails is English
If you find yourself happy with the outcome, that's the choice you go with.
If you find yourself disappointed with the outcome, go with the other.
Or flip the coin again to be sure.
You don't need Maths for Medicine. Majority of med schools won't be bothered what your third subject is - the grade just needs to be high. So maybe instead of what you enjoy most, it should be about what you will be best at for the exam?
I always advise against doing four. It can be done, but it's better to have three excellent A Levels than four good ones.