A common misunderstanding is that there are certain guidelines to follow when treating ADHD or even some other disorders. If you are diagnosed with ADHD, it is up to you to choose which path to take. Many doctors will prescribe you medication upon diagnosis: Methylphenidate (Ritalin/concerta) and Amphetamines (Adderall/Vyvanse), but it should be up to you. I would recommend finding a Psychiatrist who is willing to work with you to see how you can make the best of ADHD.

I have ADHD to a similar extent as you. Through high school I wouldn't read a single note until the night before the exam and I'd still get very good grades. I would recommend getting diagnosed because then the school can help you. If you're planning on going to University; at my University (University of Toronto), they provide accommodations such as providing you with notes and having the ability to re-schedule exams. It is very helpful!

It really depends on how much ADHD impedes on your life. If you can function fine without it, then I would recommend staying away from medication. For example, I also have much trouble paying attention to lectures and even just instructions. A sentence will float in through one ear and leave through the next, and I can never attend a lecture and take notes. My first time with Ritalin, I took it in the morning before class, went to class, took notes, and then left satisfied. I found medication most useful on days when I had laboratories and all the instructions would be explained verbally and so I wasn't able to remember much; the medication helped.

My best advice would be to find a physician who won't just toss drugs at you and tell you to come back in a few weeks for a refill. There ARE physicians out there who will look for alternative ways to help you. I'm currently on medication, but only take it on days where I know I will need to remember verbal instructions well or focus to an extent past my casual abilities.

I say see a Psychiatrist and not a GP because many Psychiatrists I've spoken to have found faults in the GP's first ritalin prescription I received (he instructed me to take one in the evening, which would impede my sleep.)

Hope I helped!