I was diagnosed with ADD at 17. It's hard to say how it's affected me especially since I was diagnosed with dyslexia at the same time so it's hard to tell.
I think socially it could explain why i'm a bit different to others. I don't quite naturally get conversations in groups and often will only hear one person so I can interupt and get confused sometimes. I didn't really have any friends between years 4 and 10 cos I just never made any after my old ones moved school.
I'll also zone out a lot or make odd links so I lost focus in lessons just as I do in conversation. It didn't have too much of an impact and I still did pretty well in school. Looking back the most obvious indicator is all my teachers calling me "a sweet little girl" or simmilar on reports cos they just didn't have anything else to say about me bad or good.
Around GCSE is where things started getting harder. I think as independant work and revision became more important my lack of focus and motivation became more of an issue. I still didn't pick up on it until college though. I realise now that I never did any homework and teachers just let me get away with it cos I was still getting the grades and always had an excuse (I viseted family in hospital for a while).
Uni was a nightmare and I left for a vaiety of reasons, but my ADD was clearly a factor. I can never get down to doing anything, especially reading. Even if i'm actually reading something I just don't take it in. I work a lot better with a practical input and I think that my teachers talking and showing videos (and putting up with relentless questions) is why i've been able to come as far as I have.
I had mh issues at the same time of all of this and i think its part of what triggered all of it. When I saw an educational psychologist though they didn't talk much about that and looked into my childhood and gave me some tests. It might actually help you to try CAMHS if you are the right age as they deal quite a bit with special needs and may have a better understanding of the relationship between special needs and mh issues.
Hope that is something like what you were looking for and good luck working everything out. One last note- look into DSA if you haven't already. You can claim it for both mh problems and special needs so you don't have to wait for the ADHD stuff to work itself out to apply.