Post gallbladder surgery 6 months ago; can't gain weight back, have dark green stool all the time, low back/stomach pain...egd/colon neg. any ideas?

S/p gallbladder: Post- cholecystectomy syndrome affects 5-40% of the population. https://en.wikipedia.org/wiki/Postcholecystectomy_syndrome For diarrhea can use Questran ,cholestyramine a bile acid sequestrant. . Avoid fatty foods. Consider breath test to evaluate for bacterial overgrowth and amylase/ lipase to check pancreas function. Discuss nerve/ sphincter of oddi / retained stone issues w/ GI doc