If it happens and your left arm feels numb, go to er. If it is coming and going, sounds more like gas.
I was getting chest pain due to milk production after giving birth, not sure how post partum you are but that could have something to do with it as well!
I had AWFUL pain in my chest (felt like a bruised bone) when I was pregnant. Turned out it was indigestion! Hard to believe but it was! I was prescribed omeprazole and it helped. May not be but it wasn’t something I’d have considered.