Are you allergic to any kind of metal, that you know of? Or it could be that your little "bout" just got through "for now" and will be back with a vengeance in a little while. Leave it off and see what happens. I don't know if there's any kind of an allergic reaction like that to a metal or not.
If I am not feeling well I don't like things around my neck, necklaces included. It may just may make you feel less restricted. I hope you feel better soon! And drink lots of fluids! Diarrhea can cause dehydration.