i agree that unfortunately that is what it's like OP, I spent many years waiting for tests, pushing for them, getting them after years, being proven right and then being devastated it got me nowhere. It is such a strain emotionally as well as physically being discriminated against because the condition is very poorly understood and not well known other than in its very mild form that is reasonably common. As you point out, there is nothing that you can take that doesn't exacerbate something else, and people just don't realise how disabling a condition it is.
It is my understanding that there are only one or two doctors with an interest in the UK, both of whom run private clinics for EDS with a wait list of nearly 2 years, and as you say, that is IF you are mobile enough, and financially able enough, to get there. I am about at the point now where I like you, cannot do it. I require my DP to go everywhere with me, and cannot drive, need a wheelchair if i am out the house but still will regularly get asked why i have one by consultants who seem to believe EDS is merely " a bit of hypermobility in the joints", rather than a connective tissue disorder and lack of autonomic dysfunction. They are arrogant and ignorant to the fact that the whole body is made up of connective tissue so it is reasonably obvious that if yours is genetically faulty, it will not be fit for purpose. My oesophagus, intenstines, and entire pelvic floor are herniated and prolapsed as a result of weak connective tissue, and even though that has been proven and there are images of this, my digestive system only functions due to medication, and i currently haven't eaten solid food in a year as I have lockjaw where my facial muscles have seized. There is nothing that can be done about the above and i get short thrift if i dare to suggest this is anything more than mildly uncomfortable (obviously it is agonising and disabling)
I was told by my cardiologist that the medications for POTS are well known to cause unwelcome side effects and was told by him that he would not take them himself. Sadly, what else can you do. I'm sorry that your issue is also complicated by diabetes so the stockings are not suitable. The only other advice i received was to add salt to my diet - though not how much, and given that i have gastroparesis and only eat once a day, there is a limit to the feasibility of that. Drinks containing electrolytes help me sometimes, or i use sports gels and rehydration salts in drinks daily. Those who think you can just ask your GP are misinformed - mine has outright said he has no idea and to try and work out for myself what works.
I am not suggesting it solves anything nor do i think it is what you want to hear but all you have got is sticking up for yourself and calling and saying you want another assessment and calling your GP/escalating the issue endlessly on the offchange someone listens. I won't be one of those people suggesting you must have it wrong and there simply must be help, because i know there isn't, and getting a diagnosis isnt helpful when you are never a candidate for surgery because of your weak tissues, or not a candidate for a medication.
I suppose the only silver lining is that everyones EDS presents differently so if you can get some sort of answer in your ultrasound then perhaps there is something that can be done in your case.
My only other advice is to consider to contact the EDS charity - www.ehlers-danlos.org - their website is very informative and at least you may be able to access advice on your situation via email, or they have a telephone advice line, as well as coordinate support groups and forums.
I think sometimes it just gets too much doesn't it. It's isolating and terrifying and awful to think you can really be that ill and there is no help, it is no surprise at all that it causes full blown anxiety. People seem to have no idea! I wish you all the best for your scan OP and hope you were able to get through the night okay.