I have chronic low back pain went to er and was given an injection of toradol which only helped for two days why?

Acute vs. chronic: Chronic pain means it has been going on for several months. By definition, this is usually not an emergency, and the er has limited resources for a problem like that, especially without new neurologic symptoms. The medication they gave you is a strong anti inflammatory, but it is not permanent. More long term treatment will depend on the cause. See your doctor or a spine specialist.

Appropriate response: The toradol (ketorolac) is for relatively severe pain but will only last for generally hours but not longer.

Potent: Anti-inflammatory injection typically gives relief for a day or two. If inflammation was reduced then likely you don't need further evaluation. Since your pain returned it suggests that either the inflammation was a lot or you created more inflammation since there is an injury that needs to be defined. See a pain/spine specialist to evaluate this further.