I agree with 1sweed, as heat does help calm the worst of the pain down. I personally take very hot Epsom salt and kelp powder baths (I add boiling water to the tub to make sure it's hot enough, but I don't let it get so hot I burn myself.) I've also found that Tens Units can help during the flare, but only as long as the machine is running. The pain comes back after the machine is done. Acupuncture has helped me substantially too, though it's not solving the problem.
For me personally, grains and sugar in any form (even as raw fruit) cause flares. I don't eat any grain, sugar, alcohol, or dairy, as all these things put me in pain. It's not an allergic response (though I am allergic to corn and wheat,) and I've read several studies showing that people with fibro don't tolerate carbohydrates or sugars well.