37 years old and possible undiagnosed autistic, hello! :)

Hi, I have been suffering with mental health issues for as long as I can remember and was diagnosed with add (attention deficit disorder) five years ago and through my most recent spell of depression, desperate to find out what is wrong with me, I discovered autism and the possibility that I am autistic.
Through speaking to an autistic friend and also doing a little bit of research and coming across this video... 
I am fairly confident that I might be an undiagnosed autistic at 37. From my research this seems to be quite a common thing!?
I know some of these questions may have been touched upon, but how long roughly has it taken most people to be diagnosed after self referral to gp? Also can autistic specific therapy make a big difference?
I currently have a therapist through the NHS, but she's a trainee and we're not doing therapy specific to possible autism. (I assume because she's not trained to)
Any help much appreciated.
Also just want to say hi! My name is Mark, from London! am hoping to find like minded people that can relate to me. From what I've read so far, there seems to be definitely a few people I can relate to on here.
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