What is likely cause been 2 years since gallbladder removal but occasionally have episodes for 2 days of stomach pain, nausea, low fever and vomiting? this time it started 1 hour after eating a burger?

You should have this evaluated by a GI doctor. Sometimes, you can have a gallstone in the common bile duct after gallbladder removal and it can cause symptoms similar to what you describe. If this is happening with fatty foods, you need to limit your fatty food intake until you are evaluated by GI. Good luck to you!

Postcholecystectomy syndrome can cause abdominal pain, nausea and vomiting, particularly after fatty and greasy foods. This is usually not accompanied by fever. See a gastroenterologist for diagnosis and treatment.