HI,
I'm sorry it's been a long difficult road for you. I don't understand why doctors can't diagnose people correctly. I've had some experience with that.
I don't know if Gabapentin would cause a rash. I'm no doctor. You can look up the side effects and see if it's on that. RSD has a lot of symptoms, not sure it that's one of them. I've been taking it for a year and it helps a lot. I had a freak accident (to long of a story) and got RSD in both feet. But currently I have it in my right foot, leg and butt. It spread from it's original spot. I might have been diagnosed from day 1 but it didn't do me much good because no one ever thought of giving me anything but morphine. I'm thankful for the gabapentin.
I hope you find a doctor that can really help you. A good one that won't think you're in it for the medication.

Geesh!
Good luck to you!!
Heather