A doctor may be able to guess if there's an obstruction by doing an abdominal examination (feeling your husband's abdomen), and it can be confirmed with a normal x-ray, that's how my second blockage was diagnosed. Before that one time I had ileus, which is a kind of obstruction (where the bowel becomes paralysed so nothing will pass through it even though there's not actually anything blocking it), and that was diagnosed the same way, examination and x-ray. With my second blockage, they then also had me drink something that showed up on x-rays so they could see how far it got through my digestive system. Then later I had another x-ray because they suspected my bowel had perforated, which it had.
But I don't think you should concern yourself about whether your husband has an obstruction or not. He's not well, and really all you need to decide is whether he needs medical attention immediately, and leave the diagnosis up to the doctors. They will probably start with basic tests: abdominal examination, maybe blood tests, blood pressure check, temperature, etc. and then they will move on to other tests - possibly x-rays or other imaging tests like barium studies, MRI, CT, etc. - if he needs them. They won't be just ruling out an obstruction or confirming it; although an obstruction is one of the more likely complications to occur in someone with Crohn's, they will be considering other possibilities, and be trying to find out what is wrong rather than just looking for a possible obstruction.
I think it would be a good idea to go to the ER. You're clearly worried, and if things are not resolving on their own it may be best for your husband to see a doctor, who will be able to give you better advice than we can here online.