bansidhe, let me share the story of my nephew's diagnosis.
When my SIL was pregnant, her first ultrasound revealed some orthopedic abnormalities. The next few months of her pregnancy were spent getting tested for various birth defects, but all the tests came up negative. When Jack was born there were many more problems than the ultrasounds had shown. He couldn't breath unassisted, there were multiple orthopedic issues that had not been visible in the ultrasounds, there were several major medical problems.
Did I mention that my SIL is a doctor in family practice? And that she had an OB doctor who specializes in problem pregnancies? And that she had the baby in the major teaching/research hospital in her area, to ensure that Jack would get the best of care from the start?
Jack has a list of 13 different birth defects and spent six months in NICU. No one had a clue as to what was wrong. The doctors involved with his care were calling and emailing colleagues all over the US for help and information, but no one could help. In the meantime, they treated the symptoms, because that was all they could do. My SIL was doing her own research at the same time. No one could come up with anything to explain the particular set of issues Jack had. And believe me, they were trying.
Finally, when he was a year and a half old, they got a recommendation to see a doctor 500 miles away, in another state, and they got a diagnosis. Jack has a very rare syndrome. He has almost none of the common symptoms of that syndrome, and pretty much all of the rarer symptoms, the ones that almost never show up.
Fourteen years later, Jack is doing very well, in large part thanks to a knowledgeable doctor who has been able to oversee his care and therapy.
The lesson to draw from this is that if you do have a rare illness/syndrome, even the best of doctors might miss it, because they don't know what to look for. It isn't that they aren't trying, it's that they might never have even heard of the illness at all. My SIL treats children all the time. She'd never heard of the syndrome that her son has--not even once in med school.
Keep asking for referrals. There is an answer out there somewhere. But you need to find the person who can direct you to the right doctor or hospital, where there is someone who has knowledge of what's wrong with you.