@TtheBee123 Hello There! To get an offical diagnosis you need to go to a psychologist in your local area who has experience in treating patients with this matter
They would conduct tests and give you recommended advice.
In terms of cost, each practise has their own rates so you might have call the office and ask how much an initial consult would cost.
To find a doctor, you can do some research on google and look at the reviews of each of the practices to make sure that their service of provided is good. Alternative you can go to your local gp and ask them to refer you to somebody. Also you might need an referral from the GP so ensure you have taken this from your doctor.
i am so sorry if my post is long just want to give you meaningful advice :)
Have a nice day!