Thanks for query,
You have not mentioned your age.
If you are elderly then there is possibility of having osteo artheritic changes in vartebrae causing backache
Go for X ray
lumbo sacral region and find out the cause.
If you are young then it shows lack of physical activity and exercise or some sprain
In any case go for back extension exercise reglarly,it will help a lot.
Use hard bed to sleep.
Take calcium and vit A,d
Ok and bye.