Fell twice in 4days, both at al apt door after using walker coming from breakfast. Went to ER and ok first time. Have 3mo old sacrum frac. Back hurts?

Vetebral fracture. If you have an additional vetebral fracture there are treatment options that can help eliminate or reduce the pain as well has maintaining quality of life. Minimally invasive procedure available is called kyphoplasty were a cement like material is injected into the fractured spine through small canulas.
Check it out. It is possible that you may have fractured one of your vertebrae, especially if you have osteoporosis, it would be a good idea to get checked out.
Full spine films?! You may have an occult vertebral fracture. If it did not show up on plain films other imaging is possible and various minimally invasive treatments.