it is incredibly frustrating not to lose weight when you cut down calories and increase exercise. It does happen that people plateau before they lose weight. Another thing that sometimes happens on the SPD is that previously someone was eating a low-carb diet which led to water weight loss. when they introduce back a normal amount of carbs, some of the water weight can come back and it feels like you're not losing weight. All I can say is, stick with it, at 1300 calories at that weight, there's no way you're not going to lose weight, but chances are with so few calories you won't keep it off because you'll be way too hungry and the weight loss will not be "real" - also, metabolism slows down at so few calories.
It's unclear what medications do to metabolism, all we do know is that meds change appetite, thirst, energy levels, and mood - all of which can contribute to weight gain and inability to lose weight.
Keep at it, and you'll see results - better slow and steady weight loss than fast and then regain.