Hi thanks for your question.
The symptoms you are having could be due to esophagitis
.Increase in acid out put and loose lower esophageal sphinter produces reflux of gastric acid
which produces oeesophagitis.There are many causes for increase acid output stress,spicy food,alcohol,smoking and infection of stomach by bacteria called Hpylori are common causes.What type of esophagitis your having only upper G I endoscopy
and biopsy can determine.Lymph node under left jaw bone is called cervical lymph node could be due to some infection in oral cavity or neck.There is no harm in getting chest X Ray done.It can explain pain under armpit to some extent.I would suggest you to consult a physician who may be able to get your upper G I endoscopy and chest X R ay done to determine the cause of chest pain
Hope this answers your question.