Since how long you have the pain? Is the pain radiating to thigh or legs?
Are you taking any medictaions?
Any past medical illness? Age and sex?
This is most likely due to compression of sciatica nerve. This is causing pain from back , it can also cause numbness or tingling sensation in thighs and legs. This is not detected in x-ray.Take Non-steroidal anti-inflammatory drugs such as ibuprofen. You should Use ice or heat to lower back for approximately 20 minutes, and repeat it every two hours.Take bed rest, and remain away from lifting any heavy objects. Also you should consult Physician for Epidural steroid injections and prescribed Painkillers. Avoid stress.