Greetings from health care magic
Bowels motion are not perfect that depends on two factor 1) slow peristaltic motion 2) lack of fibers in foods and not hydrating properly.
As you are telling you takes utmost care about your diet during travelling days then i think slow peristaltic motion is the only reason. Smooth Peristaltic motion is controlled by its muscular wall and nerve
supply. Any medications also causes constipation
So as your doctor is telling stress
yes it might be the cause of your constipation.
So practice meditation
and try to reduce stress. takr more fibers rich foods. Thank you