I weigh about the same at 5'7", and while it's technically obese as far as BMI goes, I'm only a size 18. Today, though, at 5 weeks along, I already feel huge. Not a good sign for the next 8 months! Ha!
So, Here4Support, just know that you're not alone. I'm worried about gaining weight, about taking it off after pregnancy, about finding maternity clothes that fit plus sized women and don't look like mumus or tents, etc. The list goes on and on.
Oh, and did I mention the worries about my husband seeing my true weight when we go to the doctor??? Maybe I can just get the doctor and his staff aside for a minute and say "Can we just discuss this in terms of how many pounds I've gained instead of saying -- well, you're at 260 today..." ha! How have you ladies handled that part??
As far as water goes -- my insurance company sent me a 32 oz. bug advertising their "baby yourself" program. So I fill that up 2-3 times per day and drink it. Plus, I walk about 20-30 minutes every day (I had back surgery about 3 months ago, so I have to keep it slow).