Girls, can you tell me how to get rid of pain in the lower back?

Girls, can you tell me how to get rid of pain in the lower back? Or are there any methods?) The baby is 5 months old and his lower back falls off constantly... I hold him on my hands all the time, and if I lean over him (to change or something) I can't straighten up. In my 28 years, I feel like 82 with this damn back. Don't suggest a dog fur spine ))))