HELP PLS. Crazy Stabbing pain on lower left back???

37 weeks. When I move my leg or try to walk on it I get this stabbing pain that shoots up and hits this point on my lower left side of my back. It’s really low like almost on my butt cheek. It feels kind of like my pelvic bone or like a joint in there or something it hurts so bad I literally couldn’t walk I don’t know what is going on the doctor tried to pass it off as just a muscle but oh my God that is not it.  I tried to stand and it was like my leg literally gave out. I literally can not stand on it now, it’s immediate horrible stabbing pain right at that point on my back anytime I move my left leg.