How to study ?

Hello! I need some kind of advice on studying. I dropped out of my university and applying to med. major , because I couldn’t understand math/calculus and was failing over and over again. Also I had a problem with how I study and with discipline. So this is the main question. How to study if you lack discipline, and have ADHD. I’m officially diagnosed, but my doctor said that I don’t need medication(in my country ADHD is not considered as a disorder which needs medication) So it’s untreated. And because of my adhd I struggle with procrastination and focus(obviously, I know)

And in economics major that was one of the reasons I struggled hard there(Also because I’m crazy bad at math , and not really interested in economics) Now I’m switching to medicine major, and I’m really looking forward to it , as I always thought of it , but was always scared of too much information to memorize and me not doing enough, procrastination as always , etc.

So I want to ask , how do you discipline yourself. I thrived at school , especially before exams. Because of control from teachers , parents and constant pressure. But in university no one is going to remind me about assignments, no one going to nudge/scold me about skipping lectures/not doing assignments. And that ruins everything for me. If I’m not being looked after by someone else , I just forget/ignore/dont do it.

Does anyone else have similar problems? How to solve them ? How to study ? Thank you in advance