Why do the doctors believe he has a pinched nerve in his lumbar spine has he had X Rays or an MRI if so do the findings indicate a pinched nerve.

A pinched nerve is a common diagnosis when its difficult to find the cause of back pain and its very often difficult. Patients are often given pain killers and told to live with it. I am not saying this is the case in your situation the doctors may have good evidence to support there diagnosis. But i would like to be sure of the evidence myself if i was in your situation.

If there is no serious pathology like ruptured or bulging disks or compressed nerves or stenosis then Chiro pysio or ostoe's can be helpful but beware all these therapist's will offer treatment they have nothing to lose they always get a fee unless you do a runner, so be careful and try to find a good one.

If there is serious pathology then consulting with a specialist could help.

The doctors may be absolutely right but i would not just sit back and take their word for it

gentle sensible exersice can also be helpful