Waist Pain
There are a lot of things that can cause back pain. You could have strained a muscle or tendon in that area. You could have an irritated nerve from wear and tear to your discs or through an injury.

Causes

Overuse such as working out or lifting too much, prolonged sitting and lying down, sleeping in an uncomfortable position, or wearing a poorly fitting backpack.

Self-treatment:
Physical discomfort occurred on the spine or back, ranging from mild to disabling. If the pain is severe, resting for up to two days may help.

Seeking medical care
See a doctor immediately if you;
*Experience a trauma such as a car crash or fall
*Develop a fever
*Feel intense or constant pain
*Develop pain that extends down one or both legs
*Have weakness, numbness, or tingling in one or both legs
*Can't work, sleep, or perform daily activities.