My daughter was having a problem with her wedding and engagement ring (white gold, not sure what karat). When she got the engagement ring she wore it for a year and a half with no problem. Then they purchased the matching wedding band and it didn't quite fit so both rings were taken by the jeweller to be remodelled so they would work as a set. When Katie got them back she couldn't wear them for more than a couple of hours before she had a problem pretty much like the one you describe. She tried a couple of things - one of them coating the gold on the rings with clear nail polish - with no luck. Her husband was upset as she wasn't wearing her wedding ring.
She went back to the jeweller again and had the rings sized up, just a small amount, and soldered together. We think what was happening was that 'stuff' (soap, glue, paint, etc.) was getting caught inbetween the two rings and causing a reaction of some kind. Now she can wear them no problem and everyone is happy again
I don't know if you have one or two rings so I just mention this as a possibility.