Problem while deep breathing. This be?

It was in october, i felt a mild pain while deep breathing. Whenever i take deep through nose, i feel pain going from breastbone/ chest till shoulder. And i also i feel pain between my shoulder blade and sometimes , i feel pain in my left hand too.Sometimes it goes away i feel alright and sometimes its unbearable. I have been to pulmonologist he suggested me to Esofag D before meals and lactihel syrup at bed time. I didn't feel anythingz then i went to cardiologist, my ECG and BP all were good. He asked me to change my fitness plan and take care of diet. I just remember i started exercise on my own and did it for almost 5 days before i felt the pain. I am so worried because this pain ain't going. What could this be?