Eating back exercise calories

Hi,
I'm stuck on a plateau at the moment after losing 13 pounds and I was looking for a little advice.
I consume 1200cals a day. I exercise moderately and burn about 100-200 cals a day off, but I don't usually eat those calories back.
I'm starting to wonder now if I should be doing. By burning some off I am reducing my net calories to 1000-1100 a day, and MFP tells me that below 1200 can put your body in starvation mode. I wonder if that is happening, and I wonder if anyone has any advice to share? I have started to mix up my exercise a bit but haven't tried anything new with calorie intake.
Thanks

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