If you lost weight very quickly by significantly undereating (undereating would be considered less than 1, 200 calories, which it does not sound like you did if you were eating 1, 600 calories per day), you might see a temporary drop in metabolism, and this could respond to a moderate increase in calories, but I don't think that's the case for you.

CNN: What's the best way to 'kick-start' my metabolism?