Thanks for writing to the forum!
Crohn’s disease, diverticulitis, infection in kidney, kidney stones, constipation, and an abscess in rectus abdominis muscle or psoas muscle can all cause lower left abdomen pain. It could also be a periumbilical hernia that has got trapped resulting in small bowel obstruction or mesenteric ischemia. An ultrasound or CT scan of abdomen is definitely required. Aortic aneurysm too can present this way. In women other causes can be ovary involvement, ectopic pregnancy, or endometriosis. Left flank pain is generally due to kidney stones.
I think you should discuss these possibilities with your doctor. It is difficult to comment beyond this without examining. A comprehensive investigation is required keeping all the points in mind. Hope this helps. Do let me know if there is any thing else and keep me posted. Take care!