Pain and discomfort on the lower left side of abdomen just below and to the left of navel can be due to several causes such as Crohn’s disease, colitis, diverticulitis, infection in kidney, kidney stones
, adhesions, polycystic ovary in females
, IBS, constipation, and an abscess in
rectus abdominis muscle or psoas muscle. Since you do not have a lump or a tender hot spot, in all probability it is not a muscle.