My husband has frequent urinating at night and lower abdominal discomfort. What could this be?

See Urologist soon. He could be having distended bladder with urinary retention. He needs to be evaluated by an urologist to rule out obstruction to the urinary flow by an enlarged prostate or something else before he end at the emergency room with complete obstruction.
Check the prostate. A common cause of these symptoms in a male would be a problem with the prostate gland. Another possibility is a urinary tract infection. A full history, including patient age, duration of syptoms and further description of the pain are important. Your husband should see the family doctor to obtain treatment and/or further testing as needed. Don't delay.