I have something like that at times. My dr calls it chest wall pain. Some people call it costochondritis, which i think i read is one of the types of it. It includes difficulty breathing, coughing (though i usually do not), chest tenderness, swelling and sometimes chest bruising. I first had it when i was pregnant with my dtr (she is now 25) and my mom had it when she was pregnant with me. It can feel like a heart attack. I was told if i ever had a doubt whether or not heat attack, assume it is and get it checked out. THis was before i had heart problems.
I get it when i use my left arm much. Such as picking up one of my small dogs or when dh helped me stand up one day and pulled on that arm. I can not lay on that side when it is doing its thing. Breathing is difficult as each breath hurts.
I am not saying this is your problem but if it gets any worse, please at least call the dr office for advice.