Stagnant Weight??

I first started seriously tracking my calories back in December, and since then I have lost a good amount of weight. However, in the past month or so i have been doing a pretty good job of eating about 1200 calories a day (there were definitely a few bad binge days but on the whole it's been pretty good) but my weight has not dropped significantly at all. I tend to stay away from the scale because my weight fluctuates a lot day to day and even within the same day,depending on when i weigh myself (a few days ago in the morning I was 114.2 and just now i was 117.2), but just looking at my body nothing has seriously been changing.

Should I eat more? I get full really quickly now and if I eat more than i do now at a meal i feel awful. I drink a lot of diet coke and sparkling ice waters, I wonder if that has something to do with it? I go to the gym as often as i can and do about 40 minutes of cardio 3-4 times a week. I'm getting seriously frustrated with working so hard and seeing barely any results. I'm a 5'3" 18 year old girl weighing around 116.

Please feel free to look at my diary, any advice anyone could offer would be greatly appreciated!! :)