Try a different starch

Try a different starch. Some people who I've read experiences/stories have noted similar problem: becoming intolerant (temporarily, hopefully) to a starch they have been eating often.

Maybe you could try, for example, cooked buckwheat, or buy some quinoa flour and bake a simple pancake with that. the idea is to pick some other safe-sounding starch, and try it instead of the brown rice that now seems to be cause you trouble.

(I'm not into the entirely starch-free diets some people advocate, but each to his own)