Welcome!

Thankfully for me I have not had the lifetime of problems that you have had. However I did have a childhood head injury which I am certain has made me more susceptible to future injuries (ie I don't need to be hit as hard as other people to get concussed), culminating with my current post-concussion syndrome.

Whenever I suggest to a doctor that this susceptibility has its roots in my concussion aged 9, they clearly think I am bonkers to even consider it. But the evidence on concussion in high risk groups such as jockeys and American Footballers shows that once you have had a concussion, you are more likely to get another, even after a supposed 'full recovery'. I guess doctors just don't seem to know very much about head injury, which is suprisingly common.

What I am getting at is that whilst I (obviously) couldn't say for certain, I don't think it is at all unreasonable to suggest that your difficulties may have stemmed from your childhood accident, since the effects of these sorts of injuries on the brain can be very long lasting and difficult to diagnose. And if a doctor rejects this possibility out of hand without seriously considering and looking into it, it is because they don't understand head injury.

I really hope you are able see some improvement and get some peace of mind on this issue soon.