At your weight it's going to be harder to lose lbs by the scale, even as your body gets in better shape from the exercise.
You really really have to watch your intake carefully and manage your calories. At your weight, I'd say 1300-1400 calories a day is the maximum you should be eating in order to lose healthily. That's tricky, too, because you don't want to go under 1200 either, in order to be healthy.
That's the biggest problem with trying to lose weight when you're petite and already down in the low 100s - calorie control is so crucial.