I felt my low back crunching when having a bm, i could barely walk for 2days. now when i have a bm, my lower back gets sore. what would cause this?

Back pain with BM: Are you constipated? hard stool.? drink fluids 2-3 liters/ day and have 1 cup oats or barley or brown rice or lentils a day . Pain is concerning , could be disc if strained too hard, and now get irritation from the increased pressure during BM or could be colon pathology.Would f/u with doctor get LS spine films and get a colonoscopy . May need CT of abdomen to r /o mass/ovarian. f/u with doc