What organ is under the bottom edge of the rib cage on the left side of the body? Pain from a knot under the bottom edge of the rib cage on the left side of my body. Once the knot goes away so does the pain. Getting worse. I am also a chronic pain patient

Consider Colon Spasm. Organs associated with left side of body beneath anterior rib cage are colon and spleen. A "knot" could be somatic (muscle) dysfunction related to visceral (organ) disturbance. If persistent, get abdominal x-ray, us, and/or ct scan. If intermittent, consider colon pain due to gas or spasm. In this case, use high dose of good quality acidophilus, along with bulk laxative (psyllim). Take separately.
Spleen. From your description I am not sure what you may be experiencing. The area you indicate is that of the spleen. The descending colon also starts from that area. Make an appointment with your primary care physician. Your doctor can take your history, examine you, and order any necessary tests to make a diagnosis.