If he is up late reading up on gardening tips then he's cheating on you. If he is up late reading news about the political climate, or job hunting, then he is stressed out.
I am having insomnia right now. I couldn't get to sleep until 3 hours after going to bed. I've been doing that the last week or so because I'm feeling stressed out about my relationship - at least not the immediate one; the one that we live day to day. That one is going well. The part of the relationship I'm worried about is in the long-term, because I want to move closer to my family (1000 miles away) after living up here to be with her for 11 years (I have no family here), and she is not willing to go. We have no children, I've been trying to get her to have a serious conversation about moving the last 8 years, and it can be done financially... but she still is not willing to go. I gave her an ultimatum - I want to move there by fall. She obviously didn't like it. We have been an exemplary couple, but I have no idea why there is such shear unwillingness, hesitance, and absolute refusal - other than her insecurities. Tomorrow we see a marriage counselor (after two weeks of conflict - finally), but while she sleeps soundly, I am worried because I might have to leave her or else I won't be happy (I'll be unhappy if I leave her too, which is the paradox that keeps me up at night).
It is quite possible that your husband is stressed out. But I firmly believe that before you tell others what is going on, that you tell the one you love what is going on first. If their answer doesn't satisfy you, then you seek a second opinion. So basically, tell him your concerns and ask him what is going on. His answer might be sufficient. If not, come back and tell us what he said!
He might have trouble opening up at first. Men are stubborn that way sometimes about their emotions. They don't want to admit to the family unit that he is losing cohesion within himself. That he's having anxiety or second thoughts about his ability to provide or be the man of the house. You're going to have to get him to open up. If he does not open up no matter your efforts, then you need to be concerned that the problem is concerning you and he doesn't want to tell you.
I also want to bring something up to your attention that you wrote:
Things have been great up until about 6 weeks ago.
I lost my job a few weeks ago and have decided to stay home for the summer since day care is so expensive for my daughter.
So his stress started about the time when you lost your job? Not much of a coincidence there. The other thing that stands out about your statement is that you said you
decided to stay home for the summer since day care is so expensive. Is that something you just wrote, or is it a decision you came to together? If you didn't, he could be resenting you for taking it upon yourself to make the decision about family finances all by yourself. Your actions make sense to me, but maybe they don't make sense to your husband. Just a thought...