Hi Ray, are you taking any analgesia for the pain ? I'd hate to second guess your GP, who know's more about your health than me, but I think I'd rather trial some simple painkillers, before trying an injection. There are several ones out there which should be ok to use before flying, (with the usual warning that you check with your ame blah blah).
Again, without knowing the specifics of your case, the evidence points to chiropractry, weight loss,and exercise, as effective interventions.
Physiotherapy, x-rays and rest are less effective.
PS they tell me that people who swim regularly hardly suffer back pain.