Not that this will help or be of much comfort, but some times they don't know and are still trying to figure it out themselves. It doesn't mean you shouldn't keep pushing for answers, for help, and care to manage and treat symptoms in the process. The body can be such a mystery at times especially with autoimmune things if that is what it is. Keep on the doc and go for other opinions too if necessary and in the process to find the care you need.