Feels like air or a bubble trapped at the pit of my stomach below sternum, nausea at times. can burp at times, others times can't. no appetite.

Having the sense: that air is trapped in your chest/lower esophagus can be alarming and uncomfortable. It can be due to GERD (gastrointestinal reflux) where acids/stomach contents backwash from the stomach into the esophagus. Or it can result from air swallowing (aerophagia): eating/drinking too quickly can contribute as can anxiety, talking while eating, chewing gum. carbonated drinks. Work on these; then to Doc.