What subjects are best?

Hey hey TSR

I'm getting my GCSE results in 2 weeks! Anxious, but I'm wanting to take medicine.

So for medicine I realise I need to take, Maths (I know not essential, but still), Biology and Chemistry.

That's all cool. But... I was going to take another A level, either Business or Economics. Which one would be better if I decide to take a forth?

Also, I did my GCSEs at an independent school, my Sixth Form was going to be a Selective Grammar near me, however, I have an colectomy (entire colon removal) on Saturday (Colitis sufferer, SO to the other sufferers on TSR) and my mum was thinking just to put me in the local Sixth form to which a few of my friends are attending so i can relax a bit on studies for the first sixth or so months, it's still ofsted Outstanding - but it's not selective or anything. The doctors said I should really take a few months off school post-op. But it's A-Levels, not going to risk that

Now me never have gone to a state school, are we allowed to take 4 subjects for A-Level, as the school website doesn't have any information and they are closed for any inquires until September. Say I were able to take 4, should I, or should I just stick with the base 3?

Much appreciated guys