So I've been seeing some discrepancies on the scale lately which seem to only be explained by water weight (an increase in ~3lbs over only a few days, with no bingeing etc. to cause it). So it can be one of three things: salt, TOM or stress. I don't think its TOM (but can't be sure because I'm a little irregular), and I don't think its salt, but I can test that. So then I realized that in the past week things have gotten really stressful in my life (end of semester crunch, among other things) and I'm wondering if that could cause me to retain water.

Any ideas?

I doubt it. I'd look to salt and drinking more water and only weighing once a week if you can't handle weight fluctuations.

For me the 2 biggest causes are increased water retention when I do a lot of exercise and (TMI) waste.

My weight regularly fluctuates 10lbs during a week. Don't worry about, focus on behaviors. If you try to micro manage a 3 lb jump when you've been eating right and exercising, you're wasting a LOT of mental energy...