Welcome to the community Kate. I have a lot of similar problems to you.....I know how you feel. I am 50 years old and only got a diagnosis about 8 years ago now. I've had problems like this all of my adult life. I have the same migraine/neck pain feeling sick etc you describe....the incontinence has happened to me as has the diagnosis of irritable bowel. I have the migraine with extreme visual disturbances and even began having seizures. Nothing shows up on MRI's......last neurologist I saw described my brain as 'pristine'. It's been sort of diagnosed now as meningeoencephalitis so not migraine at all really.
I have a great doctor now though it took a lot of going round the houses. I was diagnosed before I ever got to see him with Behcet's syndrome which is an auto-immune disorder. Even after diagnoses I still had trouble getting treatment that worked for me.

I do hope that will happen for you. I know how you're suffering. It may be worth you seeing an immunologist if you haven't already seen one as that's how I finally got my diagnosis.