Hello,Welcome to health care magic! The pain in the top portion of your left chest which gets aggravated by deep breaths can be a simple muscle spasm. There is a possibility of a pleuritis
also wherein the outer layer covering the lung might be inflamed. So check with your physician with an x ray
to see if anything is abnormal inside the chest. it can be just an inflammation of the bones where the cartilage
Ribs unite which might need just analgesics whenever necessary. So do not be perturbed by it but just eliminate the potential causes of this pain and be reassured. Take care!