I lost 20 pounds in a month. Once. I went from doing nothing for a couple of years to exercising daily AND a major diet change. Most of that weight was shocked off, I think. After that, I was losing 2 pounds a week. My latest round -- I have no idea how much I've lost or how fast. Really don't care to know either. Diet, diet, diet is key (not in terms of reduction, but what you put in.)
One thing I did while studying were push-up/sit-up breaks. 5 minutes, gets the blood moving, and helped my physical fitness scores. Thinking it would help your metabolism stay higher.