I suspect that I have ADHD. My girlfriend and friends do too. But I am living in the Netherlands, and my experience with doctors here has been somewhat underwhelming. For example, my tinnitus had a spike that lasted over a year. I spoke with three different doctors during this time, and none of them agreed to refer me to a specialist to have tests done to identify the source. They told me "It's common, it's incurable, you'll get used to it. No point in doing tests. Good luck".
So, from this and a few other experiences with doctors, I really don't know how I would approach getting professionally tested for ADHD - or if it is even worth it at this point. It's kind of like "Oh well, if I made it this far...." - and I suspect that that doctors would apply the same logic. But an ADHD diagnosis would help rationalize a loooot of annoying things about me, and treatment could be very helpful.