Lots of green leafy veg will help! I suffered really badly at first when I went veggie, I was so bloated! From reading up on it, what happens is your "normal" food digests quite slowly, particularly if you're eating a lot of meat - it can take weeks to fully digest apparently

So when you then start eating more healthily, easily digestible foods, you get a bit of a back up. The higher quantities of veg are digesting quickly, but can't get past the meat/stodgy food, which can make you bloated and constipated!
Green leafy veg will help and beans/pulses cos they're full of fibre! It just might take your body a while to get used to the change in diet - I know it always takes mine a while!