I feel like someone is squeezing my chest. what are the possible causes of chest discomfort?

Multiple: Chest pain involves the skin, the muscles, the bones, the cartilige, the aorta, the lungs, the esophhagus. The stomach the heart envelope, the heart muscle, the arteries of the heart and the diaphragms. Any area can produced chest discomfort.

The list is long: Angina, caused by insufficient blood flow to the heart, is at the top of the list. However, depending on your age, gender, and risk factors for heart disease, other common causes include: stress or anxiety, acid-reflux, muscular tension (sometimes due to subtle changes in activity, seated position, or carrying bag and not necessarily lifting barbells!), asthma or copd, and costochondritis.