I suspected you would have been tested already! Oh well...

Have you thought about trying an elimination diet? My mum and I did it to find out what was causing her GI problems about ten years ago, and it was really interesting. She had had a food sensitivity test, and it decided about a dozen foods were off the menu...a dozen major foods that mum wasn't happy about! So we tried this, and found that actually it was a few key foods that made her feel dreadful, not the whole lot. Interestingly, it's quite common to have a problem with vegetables from the deadly nightshade family....one of which is potatoes.

It might be worth a try, there's loads of info on the net, but this site seemed the most clear and talked some sense about it:

http://www.precisionnutrition.com/elimination-diet

If nothing else, keeping a detailed diary of your food intake and symptoms can reveal some surprising patterns. I did it for a few months to try and convince my doc that I DID have a problem with gluten when he kept denying it. Grr.

Really good luck, gastro problems are horrible at the best of times - when dealing with CRPS as well it's utterly miserable. I hope you find a way through this and can feel a bit better soon.

Bram