Unfortunately it is impossible for a woman to gain 2 lbs of muscle in a week. HOWEVER, when you begin a strength training program, your muscles tend to retain water. Depending on where you are in your monthly cycle, you could also be retaining some water from that. If you have been eating 1100-1200 calories, I highly doubt you've gained any fat. I'm willing to bet it's all water weight, so just be patient and you will see a loss soon. :)
Also - you really shouldn't eat below 1200 calories!