The important thing is that you've been tested and seen by a doctor. There is a condition that causes chest area pain. See the following link. When you see your doctor, ask for more specifics on what may be wrong, it may help ease your mind to know what is, rather than what is not, causing it.
Perhaps following up with a cardiologist that can examine all the test data that you've already had and make suggestions may also ease your mind.
"The pain usually will be sharp and located on your front chest wall. It may radiate to your back or abdomen and is more common on your left side."
Other causes of chest area pain, partial list.
Gastrointestinal: Gastroesophageal reflux disease, Gastritis, Esophagitis.
Musculoskeletal: Fibromyalgia, Reactive arthritis.
Psychogenic: Anxiety disorder, Panic disorder, Hyperventilation.