My weight has been pretty consistent..either losing or staying the same. But what reasons could there be for it going up 3 lbs? I eat the same amount of calories everyday, and exercise at least 40mins. So could it be water weight or bloating?

Given that we are mostly water, water fluctuations are very common!! Exercising can make us retain water... as can eating salty foods... all sorts of things!! There's a sticky about water weight issues at the top of this page that has more information.

Where are you at in your cycle? I go up a few days before my period, and go up again during ovulation. So twice a month for a few days. I can definitely feel it, the bloating.
Then as Heather said, there's the sodium possibility, the sore muscles, etc.

Yes, my periods starting in the next 3-6 days.. And i always feeel really bloated around this time. So I guess it could be a mixture of that and retaining water... It's just really unmotivating looking at such a gain in the scale when I've been working my butt off.