How to get a diagnosis/treatment/medications for it?

I’ve had ADHD for my whole life (I’m 23) even thought I never had a proper diagnosis for it, I’m pretty sure I have it, I always had many failures in subjects at schools and really have a high difficulty to focus/concentrate in class, is it a way that I could have a diagnosis/medications/treatment to cure it?

How to get a diagnosis/treatment/medications for it?
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