Lymph nodes are throughout the body and often become swollen if there's some infection nearby. You probably remember the doctor checking the nodes in your neck area if you went in for a sore throat. With a breast exam, the doctor will check the nodes in your arm pits. Take the antibiotics and see if that helps. If the doctor suspects diverticulitis he may want to do a colon scan (sigmoidoscopy or colonoscopy).
You said it's not an ovarian cyst. Did you have an ultrasound done already?
Yes, there is some tenderness. My GP said that it could possibly be Diverticulitus and prescribed antibiotics to see whether that helps, but the lump and tenderness is still there.
What could cause a swollen lump node if it is a swollen lymph node?
Perhaps some fecal matter since the descending colon runs down the left side. Or a swollen lymph node. Is there tenderness as well?