It might be an allergic reaction. Do you have shellfish allergies? Are you allergic to sulfa drugs? If so, then you are probably allegric to some or most types of sulfur.
I went to a health food store looking for MSM, and the guy told me that people who are allergic to shellfish (like me) can also have allergic reactions to MSM. The reason is that most MSM is made from shellfish derivitaves. Remember that MSM is sulfur, and shellfish has a lot of sulfur, so that's where a lot of MSM is made from. Also, people with shellfish allergies are allergic to that sulfur family - I think they are called sulFATES.
There's another family of sulfur, called sulFITES, that a lot of antibiotics are made from. Antibiotics like Penecillan (sp?), Bactrum, etc. (also referred to as sulfa drugs) are in that family. In reading up on MSM, I came across this warning "Those with known allergies to sulfa-containing medications and/or sulfites should avoid sulfur supplements as a precautionary measure."
One thing to note is that sulfur, by itself, is not toxic to the body. With shellfish allergies, it's the COMBINATION of a particular protein with the sulfur that causes the allergic reaction. And with sulfa drugs, it's the combinations that cause the reactions. So, the obvious solution would be to find PURE sulfur, right? However, I'm not sure that the sulfur that is available in these supplements is ever pure sulfur. Maybe because there's not a cheap or efficient way to make these products using pure sulfur.
Sorry for the long post. But the reason I know all this is because I have sulfur allergies. I'm somewhat allergic to shellfish, and I have a SEVERE allergy to sulfa drugs, which I learned the hard way. I was prescribed Bactrum once. Too make a long story short, among a host of other serious side effects, after a few days of being on it, I passed out because of how sick it was making me.
I also took some MSM for a week as an experiment to see if I would react. And wouldn't you know it, after a few days, I noticed I would feel increasingly nauseous after I took it. I also tried Cysteine (another sulfur supplement) as an experiment, and that made me nauseous too. It makes me sad that I can't experience the joys of MSM like everyone else, but better to stay healthy. If you feel like you may be allergic, you might want to come up off the MSM too.