When the baby grows and starts pressing on the pelvic joints, it starts paining, while passing urine and on moving. Also, the stretching of the uterus
puts strain on the suspending ligaments and causes pain. In addition, the hormones begin to prepare the joints for delivery as the pregnancy
advances into the last trimester, resulting in joint laxity and tender movements. Pain predominant on the left could possibly be due to the back of the baby present there as is usually the case. You can discuss with your doctor for further advice and also get a sonogram done to rule out any disturbance. Wish you a safe delivery.