Pain and discomfort on the lower left side of abdomen can be due to several causes such as Crohn’s disease, diverticulitis, infection in kidney, kidney
stones, adhesions (if you had previous abdominal surgery, 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. It could also be a periumbilical hernia that has got trapped resulting in small bowel obstruction or mesenteric ischemia.