I strongly recommend that you go see your primary care doctor
about this issue. Any pain that is persistent after a month should definitely be evaluated by a doctor to help you figure out what is going on!
The list of potential causes of your pain depends a lot on where exactly the pain is. If the pain is high in the buttocks, sort of in the low back area for example, then a strong possibility is that you have a spasm in the muscles on the sides of the spinal column, known as a paraspinal muscle spasm. Similarly, inflammation of joint between the spine and the pelvis, known as the sacroiliac joint can also produce pain in this area. If the pain is not so localized at is actually running down your legs or accompanied by numbness or tingling
that is more consistent with a pinched nerve in the back.
Your doctor will perform a complete examination and help you get to the bottom of this. Make sure you mention any severe pain, weakness in the legs, or trouble with bowel or bladder control, as this information will help them figure out if there is a potentially serious problem.