Welcome to HCM
Read your prob, after 3 abortion
you should get sonography
of abdomen for knowing texture of uterus
as any kind of uterine prob , PID , cervicitis
can causeof lower backach. so you should rule out the cause. along with it you should get Xray of lumber spine for rule out any vertibral prob. discuss it with your doc n start treatment. do not worry this is curable.