GO TO THE NEARSET HOSPITAL, IT COULD BE YOUR HEART
somebody told me that you feel kidney pain there, exactly in your front left side under rib cage
I am not a doctor, but I have had pains like that and a doctor diagnosed me with Costochondritis.IF this is what you are experiencing it is not life threatening and seems to be a type of arthritis causing inflammation between the ribs. A self test you can do is to apply some pressure with your hand to the rib cage..along the edges of it. If it is quite tender, you may have Costo.
Check with a professional to confirm.
Also, this seems to be brought on by certain movements such as exercise....have you done something recently, perhaps out of the norm for you??
Usually it will come and go. You may not have anything for months or years and then it returns.....Best of luck to you