Pregnancy does weird thing to your mind. It does weird things to your personal and professional interactions. It does weird (but glorious) things to your sex life.
First of all pregnancy plays with blood sugar. I used to be fine going from meal to meal with out an issue, now I act like my mother if I don't eat every hour.
Secondly, it makes you want to push any and almost everything that wants your time as far away as possible. It works in a circular effect. Those things closest to you (ie, your toddler, spouse) can still get time and cuddly and you are ok with it. The second circle- your immediate family you start physical distancing them "Off my lap." "Don't hang on me." ect. The oldest kids have seen a lot of times and they aren't bothered by it. Some of them even enjoy this some as it matches their desire for less parental control. There are always less apron strings on kids that have lots of younger siblings.
The third circle is you immediate social network. Parents, brothers, ect. They are people you still love, but you no longer feel it is imperative to keep track of them or hang with them. This also includes close business friends or customers. Their requests for your time have to wait until you can deal with it.
The fourth circle is the rest of the world, and most of them might as well not exist. Every invitation (that is not from the first 3 groups) is turned down. And most other activities or interactions with them become on a necessity basis only.
I believe most of these changes are the hormones preparing you self for the new baby days. When for about 6-12 m you will have to attend to the new little being for 18 hours per day.
Basically one is too exhausted to do all that is necessary the first several months, then in the last several months one is too big. And please do not ask the same question more then twice or make me tell you something more then twice. By the third time, my voice is almost always raised. And if you are requesting my time or input you better realize that I am taking time away from a nap for it and listen closely so it can go quickly. My mind may be telling me your involvement in my life is useful or valuable, but my body is tell me nothing is more valuable then food or a nap right now- and yes that does include baby Clay.