Hi E.,
When my daughter was born, my son was not yet 2, and we have no family close by, so we had to tackle that problem too. (I'm assuming you don't have family near either.) What we did was ask a couple we know well at church if they would help. Our daughter was born in the middle of the night, so our son was at their house from the evening until the morning of the next day, when my husband could pick him up and take care of him. (He was busy with me at the hospital overnight, of course.)
It turned out great--my son thought is was a grand adventure, even though he had never spent the night away from us. We joked for years that the only night my husband and I spent without our kids was the night our daughter was born, and that doesn't count! But really, choose a friend nearby, pack a special bag for your son, and try not to worry too much--you'll have enough to worry about with giving birth.
About the moodiness with your husband, for us the hardest time in our marriage was probably our first year with two children. I was so weary from taking care of a baby and toddler that I didn't have much time or energy to give my husband. Perhaps something similar is going on with you? Being pregnant and having a toddler is a big job, maybe he's feeling neglected?
It really helped me to get a new perspective by reading a few books and having some heart to heart talks with my husband. Here are some of the books that helped me:
"The Proper Care and Feeding of Husbands", by Dr. Laura Schlessinger
"For Women Only", by Shaunti Feldhan
(this has a companion book that my husband read: "For Men Only")
Best wishes,
N.