What Could Cause Left-sided Chest Pain During Cycling That Worsens When Stretching My Back?

Hi Doc!!! I would like to ask about a chest pain i feel on the left side. I am a cyclist and I m doing training. I had my session this afternoon while i was riding i can feel a pain chest but it doesn t affect my performance while i ride. Its just theres a pain. And i also noticed that when i stretched my back my chest hurts alsom i dont want to be paranoid or something i just want to know what is happening. Big thanks in advance Doc!!!