Is constant pain in lumbar left side normal in 40th week of pregnancy? No signs of active labor. Pain doesn't allow for waking and sitting.

Not normal but seen. Constant back pain limiting basic activities of daily living (e.g. Walking or sitting) isn't normal; not even at 40 week of pregnancy. The weight gain, the "basketball" & surge in hormone preparing pelvic bones for delivery may contribute to the problem. Constant severe activity limiting pain should be discussed with ob. C-section is considered as the condition may interfere w/ vaginal delivery.