I'm pregnant, what is up with my husband?

So, we have been married for over a year and have a great relationship. I'm currently in my eighth month of pregnancy. We are best friends, get along great, and he has been wonderful for the most part. Always does stuff to make me feel comfortable and gives me massages, etc. My husband is very polite and doesn't have a bad bone in him. So, I'm confused as to why he is acting different. For the past few months we have had sex less and I'm assuming it's because of the pregnancy. I've not gained any weight with this pregnancy (my first) and I still feel attractive. I've noticed that he doesn't give me attention like he used to. Now, I've never been an attention whore. In fact, I hate it. I'm shy and love for that person I love to be focused on me. I'm low maintenance. Well we have been laying in bed reading or whatever and he has picked up Sudoku in the past three weeks. I thought it was just something to pass time, but have been noticing that every time we lay in bed to watch movies or something he grabs the newspaper and pen and focuses on his game. It's like tonight. I was reading the newspaper on the sofa and he's beside me playing the Sudoku. He doesn't even look up for an hour. We are watching Celebrity Apprentice and I go out of the room and come back to find his attention on the Playboy Playmate in the bubble bath. Of course, that can get his attention and make him break from Sudoku, but for some reason I can't. I've actually noticed lately when watching TV or movies that attractive women is getting his attention where as he never really showed it before. Doesn't make me feel too good. In fact it's insulting to me as I've tried lately and nothing seems to work. We have sex about once a week now and it's bothering me as we've never had problems. I'm at the point that my self-esteem is taking a hit and I'm so afraid when the baby comes that everything will just get worse and we will have no intimacy at all.