Greys Anatomy - a pictorial guide to the human body - the old version has drawings, the new photographs.
Anatomy colour in books
Anatomy and physiology books
Introduction to Psychology
Anything to do with the sciences
The history of medicine
Where there is no doctor - an actual book
The St Johns Ambulance First Aid Manual
The Royal Marsden Manual of Nursing - I've got a very old copy and I'm not sure if it's still available - it lists all the duties of a nurse.
Medicinal plants knowledge
There are several student doctors on You Tube, that have put out some very helpful videos how to study the subject.
As above concentrate on getting good grades in your GCSEs and then build from there.
PS: Amazon also does wish lists which are often completed by students, so take a look and see what they have on theirs. Do remember the library loan service, you may not need to buy every reading material.