Unexplained heart/chest pain

[zoologyisdope]

Past 2 years ive had recurring (every few months) pain where my left side of my back (behind the pec) has a sharp pain when i breathe, this pain is worsened by exercise or generally walking about. Breathing can become very difficult and I went to hospital, had blood tests x rays but nothing was found. I was told this was just 'chest pain' I was hoping someone else had a similar experience or an explanation. Thanks for reading this.