Agreed. I eat a lot of fiber now, but kind of worked my way up there. I still find that things will be a little, er...uncomfortable...if I don't drink enough during the day, but that's pretty rare because I love cold water and typically drink loads.
It definitely will pass though (egads...really not meant to be a pun!
) as your body gets used to it. Try drinking some more, and maybe cut back a little if you've taken a big jump in your intake - once things are fine and you've adjusted, increase the amount a bit more.