If all else has failed ask your dr. about lamictal. After being misdiagnosed and mistreated for years a dr. prescribed lamictal about 10 yrs ago and it's worked wonders for me, without any apparent side affects. For all practical purposes I was disabled at the time from this condition, but not since then.
lamictal works through a different pathway from other meds so you may look into it. It's an anti-seizure med but if you dig a little deeper you'll find it's been found to be effective for sfn. It was just a stab in the dark that it was even prescribed to me. It may not work in every case but it was a game changer for me. I'm new to this site but hopefully my experience will help someone else. Good luck