rocking the baby

My baby is 8 months and we still have to rock her sometimes vigorously for her to fall asleep. It's like she wants a battle to fall asleep. I see other moms just set down their babies... what can I do to fix this, my back really hurts and we can't afford a rocking chair right now nor do we have space for one. I drink an ibuprofen almost everyday now, help please I need tips 😔