The chances are that your back muscles have gone into spasm and that is the source of the pain. What happens is that the muscles contract to protect your back and they fail to release when the danger has passed. It's a very common complaint. Painkillers won't help; they simply mask the pain.

The usual treatment is a course of anti inflammatories such as Naproxin or Celebrex taken alongside Ranititine Hydrochloride sice as Zantac or Omerprozole to protect the stomach. If that fails to work a muscle relaxant/anti depressant should help as that simply relaxes the body and thereby releases the muscles. Oddly the canabis suggestion at the beginning of the thread could have the same affect but I couldn't possibly advise you to take it.

My advice would be to go back to the doctor.