"Feeling dismissed"

I felt rather dismissed to be honest.  I've been given a private diagnosis for ADHD and ASD as I'd been told it was a wait time of 12 months on the NHS (recently phoned up to see how far along this was and been told it's been bumped to 18 months).  I attended a doctor's appointment to ask about seeking medication. I've not been doing very well mentally recently to the point where it is affecting aspects of my daily life but also physically (I've been suffering with a muscle spasm for the last week from stress), which I told the doctor.

I was told I can't even discuss 'specialist medications' for ADHD without having seen a private psychiatrist as I went with a private diagnosis, even though this diagnosis has to be accepted under the shared care agreement. I don't understand if I have a diagnosis given by a medical professional WHY I am not able to discuss the route of actual treatment with my GP?

Instead I was told to go on an antidepressant I have already previously been on (which only worked for so long) until I can get a diagnosis through the NHS. It makes me feel as if my current diagnosis is not a valid one despite being done by medical professionals. I felt I was talked to in a rather patronising way throughout despite crying through the whole GP appointment from visible discomfort.