My husband suddenly started having lower back pain. What to do?

Hi doctor,

My husband is a healthy 38 year old, who does not smoke and drink. He has worked hard since he was 11 years old, and he held his current job for five years now, which includes laying carpet and floors of all kinds. He has never had any issue with his body in his entire life up until last week. The pain started suddenly in his lower back as he was lifting a bucket half filled with glue. He did not pay any attention at the time, but the next morning the pain shifted down to his left thigh and hamstring, and it is so severe he cannot even walk or sleep. He said it gets tight for five minutes at a time then loosens up. It has been like this for a whole week now, and he cannot get comfortable with anything. He went to the emergency room a couple of days ago hoping for relief, but he got a pain shot in one arm, a muscle relaxing shot in the other, and a prescription for pain and muscle relaxants. But, nothing seems to work, he uses a heating pad, baths in Epsom salt, uses Bengay, does light exercise like stretching, but the pain remains. Could there be a medical condition causing this muscle spasm?