If you can lose weight without restricting calories, it's because you have a new set point. So right now it isn't 145-150 pounds any more. And weight loss always slows down. Just enjoy your food and watch the pounds slowly fall off.
Bodies and metabolisms can vary a lot, but I think it's fairly certain most of our bodies are determed to maintain homeostasis. What your weight and compositon is depends on many factors including genetics, what you eat, how much you eat, what type of exercise you do, and how active you are overall.
I myself have a very determined weight setpoint - I have been 100 pounds (give or take 5 in either direction) for the last 8 years no matter what I am eating, or how I exercise. On primal, my body fat distribution has been changing a tiny bit and the muscles in my lean areas are more defined, but no weight changes yet.