Blimey, congrats!

Exercise - I don't. I worked out [late] last pregnancy that exercise made me far far worse, so this time I have totally given it up. It's not worth it. (BUT I eat a lot less in the first tri)

Diet - can you can the fat and try for carbs and protein instead? Just to steady it out a little? Also, I have definitely found that getting vegies in, by hook or by crook, makes a big difference.

Fingers crossed that you make it through - without too big a blowout.