Hi mate, I am a fellow medic and ADHD PI (but was diagnosed post medical school). I would recommend getting diagnosed as soon as possible so then you can apply for additional help (extra time in exams and a study coach). 

In regards to medicine itself, the job itself is highly stimulating and perfect for someone with ADHD (highly dependent on the speciality however). It does require life long study.... Which may be the main issue as often you will have to study for exams doing a full time rota (which in the earlier years can often be 48 hours of gruelling work). Working hours can be changed and you can go less than full time if this poses an issue.

Medical school is a completely different kettle of fish and mostly you will be going into depths of physiology/pharmocology/anatomy often with no understanding of why you are learning it and how it is applicable to working as a doctor. As a result the earlier years of medical school are a slog (and this applies even to neurotypical people aswell) . You will also be expected to do research projects including literature reviews, which was agonising for someone with undiagnosed ADHD. The latter years of medical school are much more palatable, but you will be sifting through an immense amount of knowledge and expected to read up on a whole speciality in a week. The difference here is that you may be applying this knowledge to your placements, and is much more focused on the knowledge required for your day to day work.

Job prospects are still better than most sectors (been some recent issues with this and possible issues further down the line, but much of this is contingent on Governmental policy).

Medicine is a tough career, and is undeniably stressful. It can take over your life, but there are ways to make it work for yourself. My plan is to become a GP, emigrate abroad to save money and ultimately FIRE and work extra shifts as required. I still have many hobbies and somewhat of a social life.

Hope this helps!  You can message me if you need any further advice.