Over the years I've come to realize that people can be allergic to anything and you can develop allergies with things that were okay before. Try not eating the possible culprit for a few weeks, than try some, if your allergic you will get a reaction. It could be something the farmers put in the animal, if this is the case, going for organic meat may help. If it's the actual meat, it's probably you, if your body cannot process the meat than it is treating it as a foreign invader and your having an immune response. And or, it is sitting in the stomach and just fermenting, perhaps you have a problem with fat absorption and enzymes before you eat will help.