Call your surgeon. If you just had your gallbladder out and are having problems you should followup with the surgeon who removed it.
See doctor. It depends on how recently your surgery was. The first few weeks after surgery can have some adjustment period, mild nausea and belching early on can be normal. You should discuss your feelings with your surgeon.
Gerd. You may have reflux that may be contributing to your symptoms.
Recovery. If the unusual burp is new since surgery, give it a week or two while you avoid fatty food and keep your meal portion small. If the smell worsens or you have persistent discomfort or new symptoms, speak to your doctor about getting an upper GI workup which may require xray studies and/or endoscopy.
Did you have a chola. A cholangiogram is sometimes done with laparoscopic surgery, retained stones may cause pain post op, symptoms as burping or feeling nauseated may relate to dietary issues or temporary billiary reflux.