The bitch may become more clingy, wanting to be cuddled and follow you closely. Apart from that there are no noticeable changes until the time she is due to whelp when she will start nesting. Treat her as normal right until the end, just split her feeds for the last two weeks so she is not too full up.
Mine will still run like crazy. I allow them to exercise as much as they want as a fitter bitch will find it easier to give birth. Obviously in hot weather they don't run as much (but then neither do the unpregnant ones!).