Weak abs - can't do a real sit-up. as belly gets bigger in pregnancy, i fear my weak abs will make moving difficult, true? like sitting up. advice?

Don't worry: Of course it will get gradually more difficult to move around in general as the pregnancy advances, but you abdominal wall muscles won't be permanently damaged or weakened by the pregnancy. You could develop a separation of the "six pack" muscles, called a diastasis recti, after pregnancy, but this is not dangerous, and will not affect you activities. Hope this helps and good luck!