How to get my doctor to listen..?

I visited my GP today for the first time. It is a new surgery that I joined after a period where I wasn't registered anywhere and been relying on private healthcare (can't afford that any more). I have autism and I find the surgery a very difficult place to navigate, especially when it is really busy like it was today. The doctor was running half an hour behind which only added to my anxiety, so by the time I got to speak to her, I was in a bit of a mess. I only wanted some PRN medication to help to manage my anxiety as I am struggling with it a bit at the moment. I don't understand why this is such a difficulty, and why I have to argue and make justifications for a handful of tablets to see me through a rough patch. I use my CBT strategies etc, quite deftly the majority of the time, but when I'm juggling 10 different things at once and experiencing extreme overwhelm, they're not always effective. I have very high baseline anxiety, so for me to go to the GP because of my anxiety means that it is really awful and stopping me from doing things that I can normally negotiate with a little strategy. I understand for a new doctor to hear their patient talk about suicide would usually merit a call to the crisis team, but I tried to explain that I am well known to the community mental health team and they are not concerned about me (in fact I was discharged a couple of months ago) so there was no need for her to go down that route. Eventually, I managed to persuade her to give me a few tablets so that I could get back on an even keel. However, she was very short with me (I think, although I often misinterpret other people) and I didn't feel comfortable talking to her about the other reason I was there. I was really hoping that she might work with me to implement some kind of support plan regarding PRN medication so that I wouldn't have to go through this again in the future if and when I needed to. I've been trying to get a GP to support me with this for some time - it was the reason I was de-registered from my previous surgery. I used to work in health and social care, and I know that many autistic people are prescribed PRN medication to cope in times of extreme anxiety (I used to administer it), albeit with a strict protocol in place (the likes of which I would be willing to adhere to) but I cannot get a GP to agree to this for me. I guess it's because every time I get there, I am an emotional wreck due to the sensory overload of the environment. It's a vicious cycle. How do I get a doctor to listen to me? Although I may not come across this way face to face, I am actually a highly educated individual, yet I only ever get treated like a young child as soon as the autism word gets mentioned. It's very frustrating.