Dear NewUK,
probiotics cannot not to work. just like that. they go over there and do their job, either colonize or not, but depending on a type and strain- they do.
the other thing is that you react to other ingredients in the probiotic supplement or to the food itself. that's what you told- you strongly reacted to Christmass food. the food you eating may not agree with you but to blame probiotics themselves is liek to blame water!
yes, you should watch for herx reactions, but you should differentiate among the sources of bad reactions.
by the way you absolutely don't need to buy msm if you want to get superstar mineral- sulphur. Get your hands on brazil nuts ( as I do) and you'll be loaded with more sulphur than you need!