chest pain when running

[justasking]

Hi, i keep getting a really bad pain in my chest when i run and its not because im unfit or not used to running because i am but it has been there for a while and i stop when it comes. Sometimes i continue for a while and its like a knife stabbing my chest and then my left shoulder gets pains too and feels a little numb. I have had an ECG before and it was normal, does anyone know of anything else that it could be?

[joko]

its probably just a stitch! it happens when you run