The most common causes of a chronic dry cough are:
-post nasal drip
Other causes to consider: heart problems, an infection or Pertussis.
You don't say how long you have had the symptoms or what type of cough you have. Have you been to a Pulmonologist yet?
Based on what little you provided, you might want to consider acid reflux as a cough trigger. Sitting can squeeze the stomach and push the reflux up. I have GERD that is "silent" with no heartburn and a chronic cough as a symptom.
You said your EGD was stable. What do you mean by that? You can still have a normal EGD and still have reflux. It just means that there isn't any damage from the reflux.
The other thing you might want to consider is asthma. Asthma can have a cough as a primary symptom.