Sounds like his appendix, did they rule this out? Since the pain is moving and he is no better, I would take him back to the ER. Obviously something is causing his pain and they need to find out what it is! He may need to see a Gastroenterologist, but it takes time to get in to see one, suggest that one check him out at the hospital. Keep going until you get answers! I wish you all the best!
If the ER said everything was fine, I would suggest scheduling an appointment with your primary doctor and getting a refferal to a GI specialist. Perhaps at that time, your primary can do another blood and physical workup and find something the ER missed. The GI specialist might be able to help because they can perform additional testing that the ER does not perform to find the source of the pain. Lastly, when you visit your primary, don't hesitate to ask for pain medication as your husband needs some relief!
Welcome to the gastroenterology community! As mammo said, it sure sounds like his appendix. If he never got it the first time he went to the ER, I would recommend bringing him back to the ER and demanding a CT scan with contrast of his abdomen ASAP, especially if the pain is getting worse.