My husband has severe lower back pain and he's not sure what it could be?

MANY causes: The most common cause of lower back pain can due to muscle strain and should heal within 1-2 weeks. However, chronic lower back pain can be caused by arthritis, spondylitis, acute fracture (pathologic), bowel inflammation (ibd), prostatitis and other causes. The best course of action is to get seen by primary care doctor to get the proper diagnosis. Hope he is better soon!

Several possible: Several possibilities from referred pain due to kidney infection or stone, gallbladder, ulcer, pancreatitis or vascular like an aneurysm v back causes that could be tumor or infection v a disc problem or even a fracture or sprain/strain depending if injury & type of injury. Look for any fever, chills or sweats, blood in urine or stool and any abdominal symptoms. If pain severe, should be seen.