My 18yr Old Son Had His Gallbladder Taken Out Over

My 18yr old son had his gallbladder taken out over a year ago because it was non-functioning. Up until about 8 months ago, he was symptom free. Now the nausea, vomiting, diarrhea, and abdominal pain are all back. He has lost 20lbs since August. He can only eat small meals at a time or he will vomit it all back up. Before they diagnosed him with a non-functioning gallbladder, he had an endoscopy and colonoscopy, which all came back normal. Any ideas on what could be going on?