Hello, thanks for the query to H.C.M. Forum.
I n you query answer is hidden.
When over feeding is there you feel pain on the left side.
However this pain is related to over feeding , but due to misconception you felt it as in breast or chest wall.
In body on the left side there is stomach and when it is full due to over eating it make pressure over diaphragm ( membrane separating abdomen and thorax ) and root supply of diaphragm and left side of chest wall to shoulder joint is same.
When due to over feeding there is irritation to phrenic nerve
( root supply of diaphragm) than all supply area will have to pain.
SAME THING IS WITH YOU.
good luck. Eat less remains healthy. Dr. HET