Generally the solution is to come up with a descriptor like "Irritable Bowel Syndrome" or "Ideopathic XYZ" - these labels basically say that "you have some of so-and-so set of commonly co-morbid symptoms and we can't pin down a cause in your case". Not useful for cures, but useful for lumping together research projects and for managing symptoms. "Chronic Fatigue Syndrome" is one such label, and may be a cluster of diseases that present similarly.

The problem is when doctors and researchers lump these things into the "crazy patient" bin and time spent helping these patients as wastes of their time, rather than just hard cases.