Back pain

when I was about 3 months pregnant i had horrible lower back and hip pain that would travel down my legs it was excruciating and I complained to my doctor and all she said was it was because my ligaments were stretching for the baby but I literally couldn't walk and it was just horrible I did exercises and took Tylenol eventually it went away for the rest of my pregnancy and just now (2 months postpartum) it happened again but worse walking even hurt and certain positions such as laying down sitting down almost everything made me hurt.. I was in excruciating pain I almost wanted to go to the ER but my husband said they wouldn't do anything besides give me ibuprofen so he talked to my doctor and again she said THE SAME THING except that now my body was going back to into place and that's why it was hurting again and to take ibuprofen so I am but it's ridiculous they haven't requested an MRI to at least make sure I didn't actually damage my back. Anyone experience this? Could she be wrong? And should I be more demanding to at least receive a MRI?