OMG I've really stacked on the weight this pregnancy. My aim now is not to put too much more on rather than trying to lose any.
Last pregnancy I found going to the swimming centre and doing laps helped a lot. At first I couldnt do many but by the end was swimming for ages - felt great and not out of breath, thought it would do wonders for labour (Then ended up having a c/s anyway - bugga) I tried to do that again this time around but somehow sprained my right arm so that was the end of that.
I eat healthily but eat a few too many 'extras" I think.

On the other hand - I tend to put on 20kgs a pregnancy whatever I do. whether I stress over eating the 'right' things all the time, whether I exercise or not etc, It sounds like a lot but it does seem to be the 'norm' for me. Even with the twins I gained 20kgs to the dot.

Some things that work well for getting fitter are walking/waddling (he he he) and swimming.
Goodluck.