I have a lower left throbbing pain (reminds me of labor contractions) under my ribs. what could this be?

Under ribs would: include the muscles in that location, intercostal rib cage muscles, diaphragm, colon, stomach, small bowel, even heart (much less likely), etc. Study abdominal anatomy online & experiment with what movements/actions consistently change the pain; intensity, location, sensation for better clues. Usually works much better to seek help in person: too many variables.