Heart burning is a symptom of GERD and reflux. Mostly not everyone with acid reflux has heartburn and also not everyone with heartburn has acid reflux. This can be caused because of intestinal motility problems. Some times they can occur because of the cardiac workouts. Shoulder pains, chest pains and unexpected back problems can occur because of the exercise stress.
For your case I would suggest you to channel a different doctor because you have not got a clear idea about
the problem and please do not stay longer!
Whatever you do, health comes first!