If you are seeing tone changes, it might be you are gaining muscle and losing fat, but since muscle is denser your total mass isn't changing.
"Starvation mode" may or may not be a true condition, depending on who you talk too, but I do agree that you should try increasing your calorie intake to 1200/day to see if that helps. You might always want to try zigzagging (1000 one day, 1400 the next, averaging out to 8400 a week). If you aren't doing cardio, or aren't doing MUCH cardio, you might want to increase that part of your workout to increase your metabolism.
Or, if you ARE doing a lot of cardio, try adding in some weight training...
Basically, change things up and see what happens.