Frustrating changing my life.

I'm really pissed right now! I have been changing my eating habits and exercising on my wii fit for 3 weeks now, and I have lost 10 lbs. Yes that is great but, at the same time I for some reason can't get enough calories in my diet. I am ranging from 1000- 1150. I don't want to add fat in and when I add the calories the fat comes with it. I am eating 5 meals a day and still not enough calories. So for the last 3 days my weight is going up and down. I am just so frustrated, any suggestions anyone out there?