Hmmm. Have you tried playing around with the other SF foods and tiny bits of protein mixed in? Cooked and mushed carrots, squash, etc are super safe. And try egg whites, fish and soy as well for protein.
Remember that if you eat TOO limited a diet some people's bodies will rebel and become intolerant of what you ARE eating! So it could get worse if you don't expand your diet.
Also, it could well be at least partly psycosomatic...our minds can have a BIG effect with food intolerances. So can you address the stress issue with something like hypno?