Generally, gallbladder attacks become more frequent over time. While they were able to see one gallstone several years ago, there may also be crystals, aka "sludge" that they are unable to see with imaging.
While it is generally true that Ursodiol is used in gallbladder cases where surgery is high risk, I have been on a Ursodiol and fish oil regimen at the direction of my GI doc and it has substantially reduced the symptoms. I am not at high risk, however my GI doc is conservative when it comes sending folks to see a surgeon.
Time to see a GI doc.