Eating 1200 calories a day/burning 600 not losing weight

Aww honey Eat more food! 1200 calories a day is fine for someone not training like you are (In my opinion, I'm no professional). But you aren't fueling your body with enough nutrients at that level. Best of luck!

if you are putting two pounds of muscle on per month you must be on some serious gear! muscle growth is a slow, long process - a woman doing everything right is fortunate to put on .5 - 1lb muscle per month - and that is at a calorie surplus - not netting 600 calories per day as the OP is (not to mention the fact that she talks only about doing cardio - nothing about a progressive lifting program!)