Hi thanks for your question.
means a portion of your stomach enters into the chest through loose lower esophageal sphinter and produce symptoms of acid reflux
.The symptoms you have described are of hiatus hernia.It is possible that during upper G I endoscopy
a small hiatus hernia was not visualised.You can take treatment for reflux disorder and repeat upper G I endoscopy after sometime to confirm hiatus hernia.
Hope this answers your question.