Self Doubt Without Diagnosis

Background info: In the past year or so, a consultation doctor said she thought ADHD, and I got a therapist who thinks I have ADHD, so I got on medication, but do not have an official diagnosis.

In other words, three doctors think I have ADHD, yet that's not enough for my brain to accept.

(The following is an excerpt from a larger thing I wrote) I keep thinking - what if I really am just lazy/unmotivated, not ADHD?

I know that simply seeking & receiving a diagnosis would help my doubt, but I keep holding myself back. The first reason is I keep thinking it's not a big enough issue to warrant asking my parents to drop a thousand on a diagnosis to tell us what we already know (even though clearly there’s a problem). The second reason simply does not make sense - it’s essentially ‘what if I go for a diagnosis and they tell me I don’t have ADHD,’ even though the POINT of seeking a diagnosis is for them to say that either you have ADHD or you don’t. If they say I don’t have ADHD, then it’s ‘real’ that I’m just lazy/unmotivated - I don’t have a ‘reason’ other than simply personal failure. On top of that, I wouldn’t be able to take Vyvanse anymore (which is a really messed up reason to be scared of seeking a diagnosis). Taking meds hasn’t magically made everything better, but I think it’s improved things for me (although sometimes I go into the self-doubt ‘I’m just placebo-affecting my way into thinking that I am seeing a difference). On Vyvanse, I am at least (usually) able to start & go through my work, and I think my focus is a bit better. It’s not much, but I really don’t want to lose it, even though (A) I probably wouldn’t lose it because it’s fairly likely I’d get a diagnosis and (B) theoretically, if I am on ADHD medication but don’t have ADHD, then I should stop taking it.

I know I should just get the diagnosis, and I know that there isn’t much (logical) reason not to. I don't know why I am stopping myself, yet I can't stop stopping myself.