1- Musculoskeletal (muscle and bone): a condition known as costochondritis, involves inflammation of the area where the rib cage bones insert into the xyphoid bone (the flat bone in the center of the chest). Usually there's pain when you press upon that area. Pain is aggravated by sneezing, coughing, deep inspiration, or twisting of the chest. Causes could be direct trauma, or from consecutive exposure to heat and cold, inducingmuscle spasm and iinflammation.
2- Pulmonary (lungs): due to pneumonia (lung infection ; associated with fever and cough) or pleuritis (inflammation of the layer that covers the lungs, pain worsens with deep breaths)
3- Anxiety: causes pressure-like chest pain and shortness of breath (mimics a heart attack)
4- Heart disease: blockage of the coronary arteries (the arteries that nourish the heart muscles) produces chest pain
In your case, it's most likely 1 &/or 3, 2 and 4 are highly improbable. Anti-inflammatory medication will help with the costochondritis; as for the anxiety, meditation and yoga are very helpful, they help you identify the source of stress and how to deal with it.