Swollen feet and weight gain

Holli
Well looks like in the past week I've gained 4lbs and my feet have begun to swell some.. :( 
My weight gain has been pretty steady thus far.. But now I'm worried that I'm going to gain like 4lbs each week for the remaining 5 weeks of my pregnancy or something! 
I've already gaine 37lbs total which feels like soooo much to me and more than average for my size, I believe, and I still have a month to go.
Maybe the extra pounds are just due to water retention? *shrug*