specialists say "shucks, I don't have more to offer you", your PCP is the person that will be guiding you through it all. I know it sounds weird but in these difficult situations often the best person to diagnose and manage this is the person who has the largest breadth of knowledge, and that should be the PCP.

One of the diagnostic criteria of FND is that no other medical or mental condition better explains the symptoms. That's pretty tough, because that likely means you have already been through the massively expensive workup. I'm so sorry!