Both I and my sister have autoimmune diseases, I have fibromyalgia and Irritable Bowel Syndrome, she has diverticulitis. My daughter also has diverticulitis. It can be very frustrating and scary at times, but the fact that they are trying to come up with a diagnosis after him being ill only 2 weeks is a blessing, most often it's a process that lasts for years. The earlier he is diagnosed, the sooner treatment can begin.
Autoimmune disorders do not go away, treatment is to minimize symptoms. What will be involved is learning to cope on a daily basis, since there will be good days and not-so-good and downright horrible days. (I'm sorry, I am not trying to scare you but prepare you.) He may develop clinical depression, a common symptom and quite understandable. Make sure he gets treatment for that as well. I don't know which autoimmune disorder they are suspecting so can't be specific, but do try to get him into a support system or group for his disorder, whether online or a place that has meetings. Talking to others who have the same disorder helps immensely. There are support groups for people living with those who have autoimmune disorders as well, so take advantage of them for you. Diet, exercise and reduced stress are very important to his feeling good, too.
If his problem is caught now and treatment lessens the symptoms he may be able to work for some time. In the event he eventually becomes permanently disabled he can then apply for state disability.
Here's a link to an article about autoimmune disorders:
http://www.nlm.nih.gov/medlineplus/ency/article/000816.htm
And here's a link to living with an autoimmune disorder, at the bottom of the article are many more links of helpful information.
http://www.everydayhealth.com/autoimmune-disorders/unders...
You can do an internet search on the specific disorder the doctor suspects, as well.
Above all your husband will need your love, support and understanding, to know you're in his corner. This doesn't mean you neglect yourself, though, because your role as caregiver will be stressful at times. I care for my elderly father who has kidney failure, so I know firsthand. Your son will grow to learn that Daddy isn't feeling well at times, but that doesn't mean they won't be able to still have lots of fun together, they will!
Please private message me if you have any specific questions, I'd be happy to help.
God bless<3