I have a lengthy post under a previous username from about Aug/ Sept 2018 with my concerns about my then 7yo at the point that I was facing that his meltdowns were clearly not age appropriate and that there may be SNs involved beyond an obvious undiagnosed dyslexia that we were having to wait for.
Last spring at 8, the dyslexia and dyspraxia were diagnosed through a private specialist organised by school costing about £300.
Last autumn, shortly before his 9th birthday, he was identified as having high functioning autism.
It was a relief to have a concrete reason underlying his quirks, emotions and a range of unusual difficulties.
The mindmap of every detail I listed and sent to the GP basically diagnosed him along with supporting evidence from school and a QB test. Because he masks so well at school, it hasn't presented as an issue there... yet... I'm the safe place where he can vent a 4 hour meltdown because being asked if he changed his reading book was enough when his dyslexia was drowning in SATs. I was pleasantly shocked that the consultant felt she had plentiful evidence to diagnose without refering on to psychology because of how good his mask is (until his function fails). There was evidence from the early days when he had SALT, and I'm glad that I did flag things up from the begining when they were just a little off and too small to join up the puzzle. If only I'd known when I had a screaming, writhing, indestractable toddler who was beside himself for lengthy periods because we didn't go to the toy aisle on a quick trip to the supermarket, or I'd drawn the car-transporter-steam-train wrong because the cars weren't arranged to his specification. I used to be totally bemused on AIBUs about the need to watch 4 year olds hawk-like when he'd engross himself in Lego for hours without blinking. 
We're still early days. Next stage is to go through the EHCP process so he can have appropriate secondary transition and select an appropriate mainstream school. But knowing is so much better. It doesn't solve the hard moments, but it depersonalises them. It doesn't absolve him, but it makes it easier to manage triggers and discuss his choices.
He's still the same warm, funny, loving, explosive tempermental, encyclopeadic, perfectionist, quirky, individual boy he's been all along, we've just got a better window into what makes him tick and to make his world a bit more managable 