All of those places that give estimates on how to get to lose so and so pounds per week are only based on just that - estimates. There is no way at all to know for sure just how your body will react. In fact you can do the same exact thing that led you to your 2.5 lb weight loss for the next 5 weeks and get 5 entirely different results.
Thanks for the help. Maybe it was so much because my body was in shock - going from zero exercise and 2000+ cals a day to 1400-1600 cals and 90 min of exercise.
At least now I know it's normal to have bigger losses once in a while.