Get your Vit d and Vit B12 level checked.
Thanks for your query.
The pain you have in your back and knee could be due to deficiency of vit D or vit B12 as your x-rays showed nothing.
I would suggest get your vit D and vit B12 level checked. After the level checked, consult your doctor or you can consult me directly through my profile. Do physiotherapy
exercises for your back and knee to strengthen the muscle and decrease the pain.
Hope this helps you . Let me know if you have any more concerns.