Hi, D. --
I'm a spiritual person, and I always say that it's important to respect your intuition. It may not be an "omen" but more of a subconscious message that's trying to break through.
Since your husband is going to have to fess up at some point about baby #3, it seems that he may as well go ahead and do that, shouldn't he? I think it will do none of you any good to live under the cloud of the future trying to hide the inevitable. Right?
You can't live your life in the shaddows - it's not honorable and it's obviously not comfortable. If this job is restricted to parents with less than 3 kids, then he's going to either need to respect that and go elsewhere or he's going to need to address it with them to tell them why they should make the exception for him. In either case, I think you're deeply feeling the weight of the dishonesty that's part of your child's life from the very start.
If pressed, your husband could always tell his employers that, due to your recent miscarriage, he didn't want to be hasty in making his decision to tell them of your 3rd child's upcoming birth. I think they should respect that there is some element of privacy that is owed to each employee, and he should state that as such.
I have the feeling that once you can put everything back on an honest and open playing field, you will be relieved of this feeling of impending doom. Personally, I'd think you're having these feelings because you're having to invalidate your child's existence in order for your husband to have this job... and those 2 things can't be reconciled.
Take care, and I wish you luck!
H.