Chronic Stress. And what should i do?

Hello I am a 34 yrs old male feeling shortness of breathing intermittently and tired for last 3 months. I did ECG echo xRay chest thyroid profile complete blood count and all are normal. Dr told me that it hapens due to stress. So I want to is it really due to stress? Basically it hapens when I go to duty and started talking with the clients and more or less I have a hectic schedule and most of the time I use to speak from 10am to 7 pm. When I feel shortness of breathing, at the same time I also feel dryness of mouth and when I take rest for sometime it goes off automatically. And during holidays I dnt feel that much of discomfort. So I wouldlike to know whether these shortness of breath, tiredness, Felin dry mouth are due to stress or anything else? And what should I do?