I’m in the U.S. and based on Pinewalla’s comment it seems like the process is a little different in the U.K.. The way it works here is you schedule an appointment with a psychiatrist, explain to them what you’re going through, and they start to get to know you and try and help based on what they observe and what you tell them. If you want to go the medication route, the doctor prescribes you something and then you get the great U.S. privilege of fighting with your insurance company over whether or not they’ll cover your medication, and you end up shelling out $200 of your own money each month. Yay. (Not all plans work like this, but decent health insurance is rare and often outrageously expensive.) I haven’t had a brain scan, but those are not used to diagnose ADHD, so I wouldn’t worry too much about that (unless there are still other reasons you wanted to do a brain scan).
I’m sorry your experience with mental health care professionals has been poor so far, but there are good, caring doctors out there who genuinely feel for their patients and want to help make their lives easier. I hope your past experiences won’t prevent you from pursuing the assistance you deserve. I have had bad side effects and allergies from past medications and was nervous about taking medication. When I told my doctor this, she didn’t push medication, but offered; she started me on a low dose so we can monitor any negative effects and cut it off quickly if needed. The down side to doing it this way is that I’m not noticing a significant difference between being medicated and unmedicated, but I’m going to stick it out and she’ll continue to increase my dose as she determines it’s safe, effective, and necessary.
You also said: “I might just have to accept the way I am and start pinpointing triggers and start looking at ways to manage them.” I think this is a good idea, whether or not you get an ADHD diagnosis or choose to take medication. Even if you woke up “normal” tomorrow, it sounds like you’ve been dealing with hurtful comments for a long time and that this has had an impact on how you relate to others and view yourself. Therapy might be able to help you sort through some of that. We can’t control what others think, but you deserve to be comfortable – and hopefully even happy – with yourself. Best wishes!