K.B.
I think this is pretty normal. I agree, though, with the poster who said that intimacy can get you through some really bad times. I am pretty sure over the years it's what has saved us in a few instances.
It is normal to be exhausted...taking care of a busy boy and a baby girl, no matter how much sleep you get, is very tiring. However, you're wrapped up in caring for them, and your husband is likely wrapped up in caring for them and you (even if it's just by being the provider) and no one is caring for your husband, if you KWIM.
So my advice is to get in there and fake it. Even if you just do it once a week. He will be happier and you can spare 30 minutes (or less if he's typical) a week for him. And if you frame it with "I am doing this to show my husband love" then I bet your drive will come back to you at least somewhat. And even if it doesn't, and it's not "that good" for you, you can just tell him, "this is all about you, honey" and it'll be ok. :) You don't always have to have fireworks, sometimes it's ok to watch the show. LOL!
Good luck!