Back ache, one of the commonest problem facing mankind, is the price we are paying for having developed erect posture. It can be very distressing for the patient and confusing for the doctor, more so, when all the relevant investigations are normal.
One important point to consider is that pain is a subjective phenomenon. A mother can go through the apparently traumatic child birth without much problem, while at other times, she may not be able to tolerate even a small injection. That is the effect mind has on the pain sensation. When one is depressed, medically unexplained pains are common.
Solution lies in understanding and accepting the problem and tackling depression
by pharmacological or other means. Human body is not just a machine, it has a mind of its own.