You describe perfectly what many new moms, and some newdads, experience. They've been so overwhelmed with " baby chores" during the day that their minds simply can't focus.
First off, I'd like you to ask your health-care professional about postpartum depression because symptoms in mild cases can be a lack of focus and lossof sex drive. Next, if your mind is going to wander, let it wander to a fantastic fantasy that turns you on. You can then give a little delicious detail about it to your husband. By discussing a highly erotic fantasy storyline, you may find you can relax back into the moment.
Another thing you can do is ask someone you trust to babysit, to simply give the two of you some quality time on your own. Don't talk about baby things, but instead about the things you two enjoy. The little break doesn't have to be for having sex; use it to go for a walk or to watch a romantic DVD together. Whatever you do, don't hide this from your husband. Let him know how much you love him but that you are a bit mentally or emotionally overwhelmed by all the changes a baby brings.