The butcher, cut off the left flank for a stew
The left flank is on the left side between the top of the hip bone and the lowest ribs. It is a place where very little protects the intestines but muscle and fat.
The "flank" when referred to in these terms means the side or sides. Therefore you would be instructed to protect the left or right flank (side) or to protect the flank (both side)
Flank
No
Some tactics used in the second battle of Bull Run were left flank and right flank.
flank
d
On the wooden boxes, flank the doorway. At left is an acacia.
He has a reversed go-faster 7 on his left flank.
He wanted to hold off the Union from attacking their left flank.
Sounds as if you are describing left sided flank pain. Typically, we see flank pain with kidney issues such as an infection or kidney stone.