Speak to your GP, tell them how you react to things and that you want to know if there is someone you can be referred to that addressed those kinds of things. Specifically things like 'I respond differently than others to [drug] and also these behaviors that are affecting [part of your life] and want to know what I can do to find out if this is something that can be addressed'. Don't say that you think you have ADHD or Autism, just focus on what you know and that you want to address it.

A lot of symptoms/behaviors overlap between diagnosis and have different treatments. For example, both Autism and ADHD frequently (but not always) have auditory processing issues where it can be hard to understand things someone said, not because of difficulty hearing, but how the brain is processing what is heard. A professional will be able to help sort out whether something is confirmation bias or an actual diagnosis.

The most important part of a disorder like ADHD is that it reaches the level of a disorder even though most people have the same symptoms from time to time! Like how everyone gets sad from time to time, but depression has similar symptoms but is completely different than just being sad.

Personally I think you have a lot of things that would be very good to speak about with a medical professional. They will be the one who can actually evaluate you and they will ask a lot of clarifying questions. For my diagnosis I also took a multiple choice thing that was a couple hundred questions in addition to multiple appointments before there was a diagnosis.

Funnily enough I did an online autism test the other day and it said I was “Highly Likely” autistic. But then it says further down the page they charge ~£2k for diagnosis from a private clinic that obviously wants to push for more profit. Who do I trust?

That is a scam and you should only trust licensed medical doctors who did not pursue your business.

I think you have been fed a ton of misinformation and really hope you speak to your GP and find out if this is something you should pursue. I won't speculate whether you have ADHD because I am not a medical professional, but that is the type of person that will be able to help. I look back and wish that I had been diagnosed earlier, but all of the experiences that led to medication reinforce the fact that it actually does help me and that it isn't just some placebo. Hell, friends I have had for decades can tell when I forget to take them!

The best time to plant a tree is 20 years ago. The second best time is right now.