Definitely, if you've gained 15 lb. in a week, see a doctor! It's not from being pregnant, I can assure you! It's also NOT normal, whether you are pregnant or not. You want to see a doctor about that. Are you on the pill or anything? I just ask because I had a bad reaction to birth control pills, they made me retain water terribly, which made my weight go up about 15 lb. in 1 month, and the pill also made my breasts larger.
I'm almost 28 weeks pregnant, that's in my 7th month pregnant, and I've gained 11 lb. from my pre-pregnancy weight to this point.