Why are you restricting calories by so much. You are currently a healthy weight for your heigth (and on the low end of healthy). You might consider upping your calories to 1200. You shouldnt be gaining weight at that amount. Especially if you're working out. I'm same height and at that weight didn't gain at 1200cal , lost weight at 1000 cal, and if I worked out I could maintain at 1500. This is my situation though. If you are concerned about it you might want to talk to your doctor.