You are doing fine. If you eating 1550 calories (and know this by weighing the food and keeping a very accurate count of it) and are giving it your all in Pilates, and walking at least 3 mph, (brisk but not huffing and puffing) the weight will come off. I eat roughly the same caloric count as you, (i'm 5'4") and continue to lose at a nice slow rate. Sure the scale will zig and zag a bit, but it will go in a downward trend. Logging on Fitday you can see that trend... don't get hung up on a high reading, just stay the course and don't give up even when the scale goes up a little, we fluctuate. I have weighed myself enough times to know!!!
For me it is hard to eat less than 1500 calories a day and remain cheerful.
Weight loss of 52 pounds