The pain is severe to make you curl up.
The location of the pain can be due to kidneys or back problem.
Kidney stones are common cause of this type of pain.
Hence a kidney ultrasound is recommended.
Otherwise, this is likely problem with the spine.
Since the the pain is relieved by the bending your knee and raising up, that suggests release of pressure on the comprssed nerve at the lower spine.
Herniated disc and spinal stenosis both can cause this.
In that case a MRI scan of the spine will be diagnostic.
Physical therapy, epidural steroid injection and nerve block injection are commonly employed to effectively treat the problem.
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