More than likely, a gut pathogen that traditional tests cannot detect. Do the Metametrix GI Effects stool test (panel #2105) and see what they pick up. Could be a parasite, either a worm/fluke or protozoa infection, could also be a rogue bacteria or fungal/yeast.
Do not let them remove your gallbladder. Use a herbal combination and check (if you can) your taurine (methionine/cysteine) levels. Choline levels control gallbladder function. You can also do a Liver Flush which should clear the sludge.
Endocrine disorders can show up with these infections.