I second that you should get properly diagnosed by a doctor and try the available medication. If the medication works for
you sustainably it will make your life that much better and easier.
To be clear, therapy and medication is the best available option, but not everybody has access to it. In that case, what would be the next best option? (That is what I am actually asking.)
Also, there are some restrictions on medication in certain countries (e.g. Japan):
First of all, IMHO it is really important to get diagnosed by a good doctor and to rule out other reasons which could cause ADHD symptoms.
ADHD is a broad spectrum and every life is different.
The next best option I could recommend is to learn about symptoms from ADHD, examine how they are affecting your quality of life and have 'physical' crutches in place where you need them. This is highly personal, takes time for experiments to see what works for you right now, and when your situation/environment changes, you must adapt and perhaps change or create new crutches.
Still, there is a lot of stuff you simply cannot fix w/o medication: Impulsivity and focus are my biggest Achilles heels.
If there is no way for you to get medication you have to learn what problematic situations will be for you and try to avoid them from the start, because there is no way you can trust in prolonged self control if you have ADHD.