For me, it hasn't been any kind of doctor at all; rather it has been the completely alternative type of health practitioners, most especially those that work with the body's subtle energies, like chakras, auras, Qi, prana, etc. My herbalist, also has helped me out a great deal.
Of course, I will still go to see a doctor and get medical tests done, so I don't advocate completely giving up on the medical establishment. However, I do think that chronically sick people in general can neglect to look in this very alternative direction, which, in my humble opinion, may be able to help them out, sometimes considerably.