Goldfinch, I am also small, though not as small as you. I found that it's virtually impossible to maintain my normal weight, exercise, and have enough energy on the amount of calories you are consuming. So, while I am not trying to lose now, I have been there, and I can say that losing a pound a week is just too tough for people who are small.
One of the things that works for me, is to periodically "mix up" or trick my body by changing how I eat. Like, do dinner for breakfast, concentrate on more protein, etc. I also have to trick my body with different kinds of exercise. That might mean nothing more than hiking a couple of days a week, or brisk walking, yoga with some brief cardio warm up, and weights/core work. Your body is a very efficient machine and is going to learn to survive on 1100 calories a day. Perhaps you should see a nutritionist. I know that at my activity level, I need to eat at least 2,000 calories a day, even though in theory, it looks like I should be able to survive on 1200. On high activity days, I probably eat more than that. My weight is stable within 3-4 lbs., but it took upping the protein and watching carbs on days I am less active.