Having severe stomach issues. nausea (especially after sugary or fatty foods), loss of appetite, weight loss, constipation, severe anxiety. all bacterial tests normal (besides a positive sibo test 2 years ago), normal endoscopy. what could this be?

Do you still have your gallbladder? When the gallbladder becomes an issue, you can have symptoms like you describe. You also typically will have right sided abdominal pain, especially after eating fatty foods. You should see a GI doctor and have your gallbladder tested. There are treatments if that proves to be the problem. Good luck!

It is not possible to tell what is going on from just a few words written in your question, but any time someone has gastrointestinal symptoms severe enough to cause weight loss, it is important to get it evaluated. I would return to your gastroenterologist or seek a second opinion with another. Good luck.