Histamine diet

Just stick with rice for a few days if it isn't causing a reaction. Your body is in a state right now where it will react to anything, regardless of histamine content. After a few days of water and rice, try some seaweed or sweet potato. It's hard to be patient, but just give it time to calm down. Are you ingesting anything else - supplements, meds, etc.? What about other common triggers (heat, cold, showers, exercise, stress, household or body products, etc.)? Are you taking anything that stabilizes mast cells? Some mast cell stabilizers can cause a temporary increase in symptoms.

I already mentioned this to you on a different thread, but when my friend with MCAS got poison ivy, she went into a major flare like you are experiencing. She reacted to everything, including water, that went into her system, for weeks. Hang in there. Soon things will calm down enough for you to handle a bit of the lower-histamine foods, but remember that the act of digestion itself can cause MCAS, especially if you have leaky gut or are in a flare already.